Composite ion-exchange membrane

ABSTRACT

A composite ion exchange membrane having a high swelling resistance and being superior in mechanical strength and ion conductivity can be provided by means of an composite ion exchange membrane including an ion exchange resin composition and a support membrane having a continuous pore penetrating the support membrane, wherein the support membrane is one which accepts the ion exchange resin composition within the pore, and wherein the ion exchange resin composition is one which contains an ion exchange resin containing, as a main component, an aromatic polyether and/or its derivative, the aromatic polyether being obtained by mixing a compound having a specific structure, an aromatic dihalogenated compound and a bisphenol compound with a carbonate and/or a bicarbonate of an alkali metal and polymerizing the mixture in an organic solvent.

This is a 371 national phase application of PCT/JP2003/013278 filed 16Oct. 2003, claiming priority of Japanese Application No. 2002-303289 andNo. 2002-303290, both filed 17 Oct. 2002, and No. 2002-312837 and No.2002-313025, both filed 28 Oct. 2002, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a composite ion exchange membrane.Specifically, the present invention relates to a composite ion exchangemembrane superior in both mechanical strength and ion conductivity(proton conductivity).

BACKGROUND ART

In recent years, much attention has been focused on novel powergenerating techniques which are superior in energy efficiency orenvironmental friendliness. In particular, solid polymer fuel cellsusing solid polymer electrolyte membranes are characterized asexhibiting high energy density and being started and stopped more easilythan fuel cells of other systems due to their lower operatingtemperature. Therefore, they are on development as generators forelectric motorcars, dispersed power generation and the like. Inaddition, development of direct methanol fuel cells which use solidpolymer electrolyte membranes and into which methanol is supplieddirectly as fuel are underway for applications such as electric sourcesof portable devices.

Membranes comprising proton-conducting ion exchange resin films areusually used for solid polymer electrolyte membranes. Solid polymerelectrolyte membranes are required to have characteristics such as fuelpermeation inhibitability and mechanical strength preventing permeationsuch as hydrogen and methanol of fuel is necessary for a solid polymerelectrolyte membrane as well as proton conductivity. As such a solidpolymer electrolyte membrane, for example, perfluorocarbon sulfonic acidpolymer membranes in which sulfonic acid groups are introduced, typifiedby Nafion (registered trademark) made by Du Pont, U.S.A., are known.

However, because membranes comprising perfluorocarbon sulfonic acidpolymer soften up at temperatures of 100° C. or higher, the operatingtemperature of fuel cells using such membranes is limited to 80° C. orlower. Heat-resistant solid polymer electrolyte membranes have beenstudied because increase of operation temperature leads to variousadvantages, for example, energy efficiency, miniaturization ofapparatuses and improvement of catalytic activity.

In recent years, as an alternative solid polymer electrolyte membrane tomembranes containing perfluorocarbon sulfonic acid polymer, activeinvestigations have been made to so-called hydrocarbon-based polymersolid electrolytes, which contain polymers resulting from introductionof ionizable groups such as a sulfonate group into polyetheretherketonepolymers, polyethersulfone polymers, polysulfone polymers, etc.

One example thereof is a membrane containing polysulfone having asulfonate group (see, for example, F. Lufrano and three other authors,“Sulfonated Polysulfone as Promising Membranes for Polymer ElectrolyteFuel Cells” Journal of Applied Polymer Science (U.S.A.), John Wiley &Sons, Inc., 2000, Vol. 77, pp. 1250-1256). Polysulfone is suitable as araw material of solid polymer electrolyte membranes because it issuperior in processability; for example, it has a high heat resistanceand it is soluble in organic solvents. A sulfonic acid group is usuallyintroduced into polysulfone by use of a sulfonating agent such asconcentrated sulfuric acid and sulfuric anhydride. It is howeverdifficult to control sulfonation reactions by this method. In somecases, therefore, it is impossible to adjust the degree of sulfonationto a desired degree or problems such as gelation are caused bynonuniform sulfonation or side reactions.

Hydrocarbon-based solid polymer electrolytes including theabove-mentioned suflonic acid group-introduced polysulfone have problemswith respect to water resistance under high humidity because they aremore prone to hydration or swelling in comparison to membranescontaining perfluorocarbon sulfonic acid polymers.

As one measure for inhibiting such swelling, a technique using mixingwith a basic polymer has been investigated. This technique tries toinhibit the swelling by crosslinking sulfonic acid groups in a solidpolymer electrolyte membrane with a basic polymer. Examples thereofinclude a technique using a mixture of a polyethersulfone-based polymerhaving a sulfonic acid group or a polyetheretherketone-based polymer(acid polymer) and a polybenzimidazole-based polymer (basic polymer)(see, for example, WO 99/54389 pamphlet).

In addition, a technique to inhibit swelling by crosslinking betweensulfonic acid groups, which are ionizable groups, with a covalent bondis also investigated (see, for example, Japanese Laid-Open PatentPublication No. 6-93114 (U.S. Pat. No. 5,438,082, EP0 574 791 B1), WO99/61141 pamphlet, and WO 99/38897 pamphlet).

All the above techniques, however, can inhibit swelling, but they areproblematic in that ionizable groups lose their ionicity through thecrosslinking reaction and, as a result, ion conductivity falls.

As solid polymer electrolyte membranes having a crosslinked structure,membranes containing a sulfonated product from a styrene/divinyl benzenecopolymer are well known for their use in early solid polymer-type fuelcells. Such solid polymer electrolyte membranes, however, did notexhibit satisfactory characteristics as fuel cells because their polymerskeleton itself was poor in durability.

Moreover, another technique is regarding an ion exchange productobtained by subjecting chloromethyl groups in a polymer to acrosslinking polymerization using a Lewis acid as a catalyst (see, forexample, Japanese Laid-Open Patent Publication Nos. 2-248434 and2-245035). The crosslinking reaction of this technique, however,requires a catalyst. Therefore, when obtaining a molding of ion exchangeproduct by mixing a polymer and a catalyst, the remaining of thecatalyst becomes a problem. In addition, when obtaining a molding of anion exchange product by treating a molding of a polymer with a catalyst,the difficulty in occurrence of a crosslinking reaction inside themolding of the polymer becomes a problem.

Thus, a technique including synthesizing a sulfonated polymer bypolymerizing monomers having a sulfonic acid group instead ofsulfonating an existing polymers and using it as a solid polymerelectrolyte is under investigation (see, for example, Japanese Laid-OpenPatent Publication No. 5-1149 and U.S. Patent Unexamined ApplicationPublication No. 2002/0091225 specification). These sulfonated polymersare advantageous because their degrees of sulfonation can be adjustedeasily and it is easy to obtain their uniform solutions. When a solidpolymer electrolyte is used as an ion exchange membrane, in particular,when it is used as a proton exchange membrane of a fuel cell, the higherthe ion conductivity of the membrane, the better the performance.Therefore, the ion conductivity increases as the sulfonic acid groupconcentration in the membrane is increased. Among the aforementionedsulfonated polymers, however, those having high degrees of sulfonationswell greatly. Therefore, when they are used as proton exchangemembranes of fuel cells, problems tend to occur such as crossover andcrossleak of gas, delamination and breakage of electrodes, etc.

Therefore, a technique to improve the mechanical strength of solidpolymer electrolyte membranes to inhibit the dimensional change thereofby combining various reinforcing materials with solid polymerelectrolyte membranes is under investigation. As one example thereof,reinforcement by blending a sulfonated polymer resulting frompolymerization of sulfonated monomers and a non-sulfonated polymerpossessing a similar structure has been proposed (see, for example,Japanese Laid-Open Patent Publication No. 5-4031). It, however, hasdrawbacks in that the sulfonated polymer and the non-sulfonated polymerare less compatible with each other due to a great difference betweentheir polarities and, therefore, it is impossible to obtain uniformmembranes.

In addition, reinforcement of a sulfonated polymer with a porous supportmembrane has also been proposed (see, for example, WO 00/22684pamphlet). However, as the sulfonated polymer, only existing polymersare listed and this publication discloses no example of using asulfonated polymer, which is a better polymer electrolyte, obtained bypolymerization of sulfonated monomers. In addition, the supportdisclosed in this publication has a drawback in that if it is fabricatedinto a composite membrane, the ion conductivity will fall due to the lowporosity of the support membrane.

Based on the circumstances, a major object of the present invention isto provide a composite ion exchange membrane having a high swellingresistance and being superior in mechanical strength and ionconductivity.

DISCLOSURE OF THE INVENTION

The present inventors obtained an idea that use of a composite ionexchange membrane comprising an ion exchange resin composition includingsulfonated polysulfone obtained by polymerization of sulfonated monomersand porous support membrane can solve the above-mentioned problem. Then,they conducted research and development actively to find out, from suchcomposite ion exchange membranes, a material possessing characteristicssuitable as a solid polymer electrolyte membrane.

As a result, the present inventors found out that it is possible toobtain a composite ion exchange membrane having a high swellingresistance and being superior in mechanical strength and ionconductivity by impregnating a support membrane having continuous porespenetrating the membrane with an ion exchange resin compositioncontaining an aromatic polyether and/or its derivative, the aromaticpolyether being obtained by polymerizing a specific raw material.

In addition, the present inventors made it clear that when theabove-mentioned aromatic polyether and/or its derivative has a specificchemical structure, the performance of the composite ion exchangemembrane is improved. Thus, the present inventors made it clear that itis possible to improve the above-mentioned composite ion exchangemembrane by making the composite ion exchange membrane have a specificstructure and, as a result, they accomplished the present invention.

The composite ion exchange membrane of the present invention is acomposite ion exchange membrane comprising an ion exchange resincomposition and a support membrane having a continuous pore penetratingthe support membrane, wherein the support membrane is one which acceptsthe ion exchange resin composition within the pore, wherein the ionexchange resin composition is one which contains an ion exchange resincontaining, as a main component, an aromatic polyether and/or itsderivative, the aromatic polyether being obtained by mixing a monomercomponent which contains, as main ingredients, a compound represented byChemical Formula 1, an aromatic dihalogenated compound and a bisphenolcompound with a carbonate and/or a bicarbonate of an alkali metal andpolymerizing the mixture in an organic solvent.

(In Chemical Formula 1, Q represents a —S(═O)₂— group or a —C(═O)—group. X represents an H atom, an Li atom, an Na atom or a K atom. Yrepresents an F atom, a Cl atom, a Br atom or an I atom.)

Alternatively, the composite ion exchange membrane of the presentinvention is a composite ion exchange membrane comprising an ionexchange resin composition and a support membrane having a continuouspores penetrating the support membrane, the support membrane is onewhich accepts the ion exchange resin composition within the pore,wherein the ion exchange resin composition is one which contains an ionexchange resin including linking units represented by Chemical Formula2A and linking units represented by Chemical Formula 2B at a ratio,Chemical Formula 2A:Chemical Formula 2B=n:m, respectively.

(In Chemical Formulas 2A and 2B, Z represents H, Li, Na, K or a cationderived from an aliphatic or aromatic amine. Ar₁ and Ar₃ independentlyrepresent one or more kinds of bivalent organic group. Ar₂ representsone or more kinds of bivalent organic group including an aromatic ringhaving an electron-withdrawing group. n and m represent an integerwithin a range of 1 to 1000 and an integer within a range of 0 to 1000,respectively.)

Here, it is preferable that Ar₂ be one or more kinds of linking unitselected from the group consisting of linking units represented byChemical Formula 3, Chemical Formula 4 and Chemical Formula 5.

(In Chemical Formula 3, Chemical Formula 4 and Chemical Formula 5, Arepresents in each occurrence a linking site with another linking unit.)

In addition, it is desirable that Ar₁ and Ar₃ each be one or more kindsof linking unit selected independently from the group consisting oflinking units represented by Chemical Formula 6 and Chemical Formula 7.

(In Chemical Formula 6 and Chemical Formula 7, A represents in eachoccurrence a linking site with another linking unit.)

Moreover, it is more preferable that Ar₁ and Ar₃ each be a linking unitrepresented by Chemical Formula 6, Ar₂ be a linking unit represented byChemical Formula 3, and n and m each be an integer within a range of 1to 1000 which satisfies Mathematical Expression 1.0.2≦n/(n+m)≦0.8  (Mathematical Expression 1)

Alternatively, it is also permitted that Ar₁ and Ar₃ each be a linkingunit represented by Chemical Formula 6, Ar₂ be a linking unitrepresented by Chemical Formula 4, and n and m each be an integer withina range of 1 to 1000 which satisfies Mathematical Expression 2.0.2≦n/(n+m)≦0.8  (Mathematical Expression 2)

Alternatively, it is also permitted that Ar₁ and Ar₃ each be a linkingunit represented by Chemical Formula 7, Ar₂ be a linking unitrepresented by Chemical Formula 3, and n and m each be an integer withina range of 1 to 1000 which satisfies Mathematical Expression 3.0.3≦n/(n+m)≦0.7  (Mathematical Expression 3)

The composite ion exchange membrane of the present invention preferablyhas a surface layer comprising the ion exchange resin composition oneach side of the support membrane. It is desirable that the thickness ofeach of the surface layers preferably be within a range of 1 to 50 μmand also within a range which does not exceed half the total thicknessof the composite ion exchange membrane. Further, it is recommended thatat least one surface of this support membrane have an aperture ratiowithin a range of 40 to 95%.

It is also preferable that the ion exchange resin composition in thecomposite ion exchange membrane of the present invention be one whichcontains a crosslinked ion exchange resin obtainable by crosslinking anion exchange resin having an ionizable group in the molecule and alsohaving a photocrosslinkable group and/or a thermally crosslinkable groupin the molecule.

Here, it is preferable that the photocrosslinkable group contain both acrosslinkable group having a chemical structure represented by ChemicalFormula 8 and a crosslinkable group having a chemical structurerepresented by Chemical Formula 9.

(In Chemical Formula 8 and Chemical Formula 9, R represents an aliphatichydrocarbon group with a carbon number within a range of 1 to 10. orepresents an integer within a range of 1 to 4).

It is desirable that the thermally crosslinkable group be at least onethermally crosslinkable group selected from the group consisting ofthermally crosslinkable groups of chemical structures represented byChemical Formulas 10 to 15.

(In Chemical Formulas 10 to 15, R¹ to R⁹ each independently represent ahydrogen atom, an alkyl group with a carbon number within a range of 1to 10, a phenyl group, an aromatic group with a carbon number within arange of 6 to 20 or a halogen atom. P represents a hydrogen atom, ahydrocarbon group with a carbon number within a range of 1 to 10,halogen, a nitro group or a —SO₃T group. T represents an H atom or amonovalent metal ion. n represents an integer within a range of 1 to 4.)

It is desirable that the ionizable group be a sulfonic acid group and/ora phosphonic acid group. Further, it is desirable that the polymer mainchain of the ion exchange resin be a polyethersulfone-type main chain ora polyetherketone-type main chain.

The composite ion exchange membrane of the present invention preferablyhas a surface layer comprising the ion exchange resin composition oneach side of the support membrane.

Here, it is desirable that the thickness of each of the surface layerspreferably be within a range of 1 to 50 μm and also within a range whichdoes not exceed half the total thickness of the composite ion exchangemembrane. Further, it is recommended that at least one surface of thissupport membrane have an aperture ratio within a range of 40 to 95%.

The support membrane preferably includes a polybenzazole-type polymer asa material thereof.

The support membrane preferably is one which was obtained by shaping anisotropic solution containing the polybenzazole-type polymer in acontent within a range of 0.5 to 2% by mass into film and thensolidifying the solution.

In addition, the composite ion exchange membrane of the presentinvention preferably is one in which when a straight line runningthrough the composite ion exchange membrane along its thicknessdirection is set in an analysis area in a cross section of the membraneand a linear analysis for elements contained only in the ion exchangeresin is conducted using an electron probe microanalyzer, the variationin the number of X-ray counted, as indicated in CV value, is within 50%.

Moreover, the composite ion exchange membrane of the present inventionpreferably is one in which when a straight line running through thecomposite ion exchange membrane along its thickness direction is set inan analysis area in a cross section of the membrane and a linearanalysis for elements contained only in the ion exchange resin isconducted using an electron probe microanalyzer, the number of theanalysis points where the number of the counted X-rays of the analyzedelements is 5% or less relative to the maximum number is within 0 to 30%of the number of all the analysis points.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cross sectional structure of oneexample of a composite ion exchange membrane of the present invention.

FIG. 2 is a diagram showing a photograph of an image obtained by drying,at the critical point, one example of the support membrane for use inthe present invention before combining it with an ion exchange resincomposition and then observing its surface by a scanning electronmicroscope.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail below byreference to embodiments thereof.

<Composite Ion Exchange Membrane>

The composite ion exchange membrane of the present invention is acomposite ion exchange membrane comprising an ion exchange resincomposition and a support membrane having a continuous pore penetratingthe support membrane, wherein the support membrane is one which acceptsthe ion exchange resin composition within the pore, and the ion exchangeresin composition is one which contains an ion exchange resincontaining, as a main component, an aromatic polyether and/or itsderivative, the aromatic polyether being obtained by mixing a monomercomponent which contains, as main ingredients, a compound represented byChemical Formula 1, an aromatic dihalogenated compound and a bisphenolcompound with a carbonate and/or a bicarbonate of an alkali metal andpolymerizing the mixture in an organic solvent.

(In Chemical Formula 1, Q represents a —S(═O)₂— group or a —C(═O)—group. X represents an H atom, an Li atom, a Na atom or a K atom. Yrepresents an F atom, a Cl atom, a Br atom or an I atom.)

Here, it is possible to obtain the compound of Chemical Formula 1, forexample, by sulfonating a compound such as4,4′-dichlorodiphenylsulphone, 4,4′-difluorodiphenylsulphone,4,4′-dichlorobenzophenone and 4,4′-difluorobenzophenone by heating itwith fuming sulfuric acid.

It is preferable that Q in Chemical Formula 1 be a —S(═O)₂— groupbecause the solubilities of the monomer and the polymer will beincreased. Further, Y in Chemical Formula 1 preferably is F or Clbecause the reactivity will become high. It is preferable that X inChemical Formula 1 is not an H atom. X is preferably an Na or K atom.

Here, preferred examples of the compound represented by Chemical Formula1 are shown as Chemical Formulas 8A to 8D and Chemical Formulas 9A to 9D(each including a plurality of chemical formulas).

The aromatic dihalogen compound in the present invention refers to acompound having at least one aromatic ring and at least two halogenatoms each bonding to an aromatic ring. As such an aromatic dihalogencompound, preferred is a compound in which an electron-withdrawing groupbonds to the identical aromatic ring a halogen atom bonds to. A compoundin which the electron-withdrawing group bonds to the ortho or paraposition with respect to a halogen atom is more preferred. Examples ofthe electron-withdrawing group include a sulfone group, a sulfonylgroup, a carbonyl group, a phosphine oxide group, a nitro group and acyano group. It is desirable that the halogen atoms be an F atom or a Clatom. The two or more halogen atoms may bond to either the identicalaromatic ring or different aromatic rings.

Here, preferable examples of the aromatic dihalogen compound includecompounds of chemical structures represented by Chemical Formulas 10A to10I.

The compound of Chemical Formula 10C, which has two or more halogenatoms, can be used suitably for polymer synthesis like other aromaticdihalogen compounds because the number of the halogen atoms whichsubstantially contribute to the polymerization reaction is two.

Among the compounds represented by Chemical Formulas 10A to 10I,particularly preferred as the aromatic dihalogen compound in the presentinvention are 4,4′-dichlorodiphenylsulphone,4,4′-difluorodiphenylsulphone, 2,6-dichlorobenzonitrile and2,6-difluorobenzonitrile. Most preferred are 2,6-dichlorobenzonitrileand 2,6-difluorobenzonitrile.

The bisphenol compound refers to a compound of a chemical structurehaving two hydroxyl groups (phenolic hydroxyl groups) bonding to anaromatic ring.

Here, preferable examples of the bisphenol compound include compounds ofchemical structures represented by Chemical Formulas 11A to 11P.

Among the bisphenol compounds of chemical structures represented byChemical Formulas 11A to 11P, particularly preferred are 4,4′-biphenoland 9,9-bis(hydroxyphenyl)fluorene. 4,4′-biphenol is the mostpreferable.

<Production Method of Ion Exchange Resin>

The aromatic polyether and/or its derivative, mainly contained in theion exchange resin for use in the present invention, is obtained bymixing a monomer component which contains, as main ingredients, acompound represented by Chemical Formula 1, an aromatic dihalogenatedcompound and a bisphenol compound with a carbonate and/or a bicarbonateof an alkali metal and causing a polymerization reaction by heating themixture in an organic solvent.

Here, as the organic solvent, highly polar solvent such asN-methyl-2-pyrrolidone, N,N′-dimethylacetamide, N,N′-dimethylformamide,sulfolane, dimethylsulfoxide and hexamethyl phosphonamide, which arehighly polar organic solvents, can suitably be used. Among thesesolvents, N-methyl-2-pyrrolidone, sulfolane and the like, which having ahigh boiling point, are particularly preferred because use thereof makesit possible to set the reaction temperature high to increase the rate ofreaction.

As the carbonate and/or bicarbonate of an alkali metal, for example,potassium carbonate and sodium carbonate are preferable.

In addition, it is desirable to dry the compound represented by ChemicalFormula 1 before use because it easily absorbs moisture. Further, it isdesirable to remove, to the outside of the system, the water formed inthe reaction of the bisphenol compound and the carbonate and/orbicarbonate of an alkali metal before the occurrence of a reaction withthe starting monomers because it will cause side reactions. Here, thedehydration inside the system may use any conventionally known methodsuch as azeotropy with toluene, benzene, chlorobenzene or the like andadsorption with a dehydrator such as calcium hydride, anhydrous sodiumsulfate and molecular sieve.

Further, the temperature of the polymerization reaction is desirably notlower than 150° C. and more desirably not lower than 180° C. Further,the temperature is desirably not higher than 300° C., and more desirablynot higher than 250° C. When the temperature is lower than 150° C., thedegree of polymerization tends not to be high enough. When thetemperature is over 300° C., many or side reactions such as crosslinkingand decomposition tend to occur frequently or vigorously.

The time of the polymerization reaction is desirably not shorter thanthree hours, and more desirably not shorter than five hours. Further,the time is desirably not longer than 50 hours, and more desirably notlonger than 30 hours. When the time is shorter than three hours, thedegree of polymerization or the recovery of polymers tends to fall. Whenthe time is longer than 50 hours, it tends to be difficult to obtainpolymers possessing desired characteristics due to side reactions suchas crosslinking and decomposition.

It is desirable to conduct the polymerization reaction under anatmosphere of an inert gas such as nitrogen.

When an aromatic polyether and/or its derivative was obtained by themethod described above, an ion exchange resin composed mainly of thearomatic polyether and/or its derivative may be used, after isolation,as part of the material of the composite ion exchange membrane of thepresent invention. Alternatively, the composite ion exchange membrane ofthe present invention may be produced by introducing the ion exchangeresin into a support membrane while dissolving or dispersion it in asolution.

The isolation of the ion exchange resin which is composed mainly of thearomatic polyether and/or its derivative may be done using aconventionally known method. For example, a popular method is to isolateit by its reprecipitation in water, methanol, ethanol, acetone, etc. ortheir mixed solvents.

It is also permitted to remove inorganic salts in advance by filtering apolymerization solution before the isolation by the reprecipitation ofthe ion exchange resin. The ion exchange resin isolated byreprecipitation may be subjected to removal of impurities such assolvent, oligomers, residual monomers and inorganic salts, for example,by treatment in hot water. Further, sulfonic acid groups of the ionexchange resin isolated by reprecipitation may be converted from thealkali metal salt form to the acid form through a treatment withsulfuric acid, hydrochloric acid and the like. After these operations,the ion exchange resin isolated by reprecipitation may be isolated byremoval of the reprecipitation solvent by filtration and drying.

<Impregnation of Support Membrane with Ion Exchange Resin Composition>

It is possible to obtain the composite ion exchange membrane of thepresent invention by dissolving the ion exchange resin isolated in theabove-mentioned manner in an organic solvent to form a solution and thenimpregnating a support membrane with the solution, thereby combining thesupport membrane with an ion exchange resin composition containing theisolated ion exchange resin.

Here, as the organic solvent, N-methyl-2-pyrrolidone,N,N′-dimethylacetamide, N,N′-dimethylformamide, sulfolane,dimethylsulfoxide, etc. can suitably be used. Among these organicsolvents, N,N′-dimethylacetamide, N,N′-dimethylformamide,N-methyl-2-pyrrolidone and the like are particularly preferred.

When impregnating a support membrane with an ion exchange resincomposition containing an ion exchange resin prepared in the mannermentioned above, it is also possible to introduce a polymerizationsolution of the ion exchange resin as received into the supportmembrane. Prior to this operation, it is also permitted to removeinorganic salts and the like from the polymerization solution in whichthe ion exchange resin is dissolved or dispersed by subjecting thepolymerization solution containing the ion exchange resin dissolved ordispersed therein to filtration or centrifugal sedimentation.

In this case, it is also permitted to adjust the concentration of theion exchange resin in the polymerization solution by optionally adding agood solvent such as N-methyl-2-pyrrolidone, N,N′-dimethylacetamide,N,N′-dimethylformamide, sulfolane, dimethylsulfoxide and hexamethylphosphonamide to the polymerization solution containing the ion exchangeresin dissolved or dispersed therein.

Here, it is possible to combine the support membrane and the ionexchange resin composition by impregnating the support membrane with thesolution containing the ion exchange resin dissolved or dispersedtherein and then removing the solvent. As to the solution containing theion exchange resin dissolved or dispersed therein, the polymerizationsolution as received may be used. Alternatively, a solution prepared bydissolving or dispersing an isolated ion exchange resin in a solventagain.

Sulfonic acid groups of the ion exchange resin may be in acid form.However, in order to inhibit the decomposition of solvents, they aredesirably salts formed together with alkali metal or the like.

The concentration of the ion exchange resin in the solution containingthe ion exchange resin dissolved or dispersed therein is desirably notlower than 5 wt %, and more desirably not lower than 10 wt %. Further,the concentration is desirably not higher than 50 wt %, and moredesirably not higher than 40 wt %. When the concentration of the ionexchange resin is lower than 5 wt %, the content of the ion exchangeresin in the composite ion exchange membrane becomes small and thereforethe ion conductivity tends to fall. When the concentration exceeds 50 wt%, the viscosity of the solution containing the ion exchange resindissolved or dispersed therein increases and therefore it tends tobecome difficult to handle the solution.

The solution containing the ion exchange resin dissolved or dispersedtherein may contain a non-solvent such as water and alcohol unless thesolution gets turbid or gelates.

When the support membrane contains a solvent which is incompatible withthe solution containing the ion exchange resin dissolved or dispersedtherein, it is desirable to replace the solvent contained in the supportmembrane by a solvent the same as that of the ion exchange resinsolution before the support membrane is impregnated with the solution.If it is difficult to replace the solvent all at once in the course ofthe solvent replacement, it is also permitted to replace the solventstepwise by, for example, immersing the membrane in mixed solventsdifferent in mixing ratio of the solvents.

When the support membrane is immersed in the solution containing the ionexchange resin dissolved or dispersed therein, the time, temperature,bath ratio and the like of the immersion are not particularly limited.Suitable conditions may be used depending on the shape, size, porosity,aperture ratio and the like of the support membrane or the chemicalstructure, molecular weight and the like of the ion exchange resin, orthe concentration, viscosity and the like of the solution containing theion exchange resin dissolved or dispersed therein.

The method for removing the solvent from the support membraneimpregnated with the solution containing the ion exchange resindissolved or dispersed therein is not particularly limited. The dryingmay be carried out by any conventionally known means such as hot blast,infrared ray and reduced pressure.

When sulfonic acid groups in the ion exchange resin contained in the ionexchange resin composition in the composite ion exchange membrane of thepresent invention are in the form of salt, it is permitted to convertthe sulfonic acid groups into acid form by treating the composite ionexchange membrane with acid. When using the composite ion exchangemembrane of the present invention as a proton exchange membrane of afuel cell, it is desirable to use it in the acid form.

In this case, examples of the acid for use in the conversion of thesulfonic acid groups in the ion exchange resin into the acid forminclude solutions of strong acids such as sulfuric acid, hydrochloricacid and perchloric acid with a concentration of 0.1 to 10 mol/L.

In the treatment for conversion of the sulfonic acid groups in the ionexchange resin into the acid form, it is also permitted to heat thecomposite ion exchange membrane of the present invention. After the acidtreatment, it is desirable to wash the composite ion exchange membraneof the present invention fully with water or hot water so that no freestrong acid remains within the composite ion exchange membrane. Whendrying the washed composite ion exchange membrane of the presentinvention, it is preferable to do so while fixing it with a frame.

<Chemical Structure of Ion Exchange Resin>

It is possible to express the ion exchange resin for use in the presentinvention as an ion exchange resin possessing a chemical structurecontaining linking units represented by Chemical Formula 2A and linkingunits represented by Chemical Formula 2B at a ratio Chemical Formula2A:Chemical Formula 2B=n:m, respectively.

(In Chemical Formulas 2A and 2B, Z represents H, Li, Na, K or a cationderived from an aliphatic or aromatic amine. Ar₁ and Ar₃ independentlyrepresent one or more kinds of bivalent organic group. Ar₂ representsone or more kinds of bivalent organic group including an aromatic ringhaving an electron-withdrawing group. n and m represent an integerwithin a range of 1 to 1000 and an integer within a range of 0 to 1000,respectively.)

Here, n and m in Chemical Formula 2A and Chemical Formula 2B, which areintegers within a range of 1 to 1000, are desirably integers satisfyinga Mathematical Expression of 0.2≦n/(n+m)≦0.9.

Here, when the composite ion exchange membrane of the present inventionis used as a proton exchange membrane in a fuel cell (a solid polymerelectrolyte membrane in a solid polymer fuel cell which uses hydrogen asfuel), it is desirable that Z in Chemical Formula 2A be an H atom. Whenthe composite ion exchange membrane of the present invention is used asa solid polymer electrolyte membrane in a direct methanol-type fuel cellusing methanol as fuel, it is desirable that Z in Chemical Formula 2A bean H atom.

In Chemical Formula 2B, Ar₂ represents a bivalent organic group havingan electron-withdrawing group. Further, Ar₂ is desirably an aromaticgroup having an electron-withdrawing group among the bivalent organicgroups having an electron-withdrawing group. Examples of theelectron-withdrawing group include a sulfone group, a sulfonyl group, acarbonyl group, a phosphine oxide group, a nitro group and a cyanogroup. Further, it is desirable that the electron-withdrawing group beattached to the aromatic group at the ortho or para position withrespect to the oxygen atom of the ether bond.

Examples of Ar₂ include linking units having chemical structuresrepresented by Chemical Formulas 12A to 12E.

(In Chemical Formulas 12A to 12E, A represents in each occurrence alinking site with another linking unit.)

Among the linking units of these chemical structures, the linking unitshaving chemical structures of Chemical Formulas 3 to 5 are moredesirable. Further, the linking units having chemical structuresrepresented by Chemical Formula 3 and Chemical Formula 4 areparticularly desirable. The linking unit having a chemical structurerepresented by Chemical Formula 4 is the most desirable.

(In Chemical Formula 3, Chemical Formula 4 and Chemical Formula 5, Arepresents in each occurrence a linking site with another linking unit.)

The Ar₁ and Ar₃ each represent a bivalent organic group. Examplesthereof include linking units having chemical structures resulting fromremoval of two hydroxyl groups from the compounds provided as examplesof bisphenol compounds in Chemical Formulas 11A to 11P.

Here, Ar₁ and Ar₃ may be either identical to or different from eachother. Alternatively, each of Ar₁ and Ar₃ may be composed of two or moredifferent kinds of linking units.

Among Ar₁ and Ar₃, linking units having chemical structures representedby Chemical Formula 6 and Chemical Formula 7 are particularly desirable.A linking unit having a chemical structure represented by ChemicalFormula 6 is the most desirable.

(In Chemical Formula 6 and Chemical Formula 7, A represents in eachoccurrence a linking site with another linking unit.)

Here, the ion exchange resin for use in the present invention is moredesirably an ion exchange resin possessing a chemical structurecontaining linking units represented by Chemical Formula 2A and linkingunits represented by Chemical Formula 2B at a ratio Chemical Formula2A:Chemical Formula 2B=n:m, respectively, wherein both Ar₁ and Ar₃ arelinking units having a chemical structure of Chemical Formula 6, Ar₂ isa linking unit of a chemical structure represented by Chemical Formula3, and n and m are integers within a range of 1 to 1000 which satisfyMathematical Expression 1.0.2≦n/(n+m)≦0.8  (Mathematical Expression 1)

Alternatively, the ion exchange resin for use in the present inventionis also more desirably an ion exchange resin possessing a chemicalstructure containing linking units represented by Chemical Formula 2Aand linking units represented by Chemical Formula 2B at a ratio ChemicalFormula 2A:Chemical Formula 2B=n:m, respectively, wherein both Ar₁ andAr₃ are linking units having a chemical structure of Chemical Formula 6,Ar₂ is a linking unit of a chemical structure represented by ChemicalFormula 4, and n and m are integers within a range of 1 to 1000 whichsatisfy Mathematical Expression 2.0.2≦n/(n+m)≦0.8  (Mathematical Expression 2)

In addition, the ion exchange resin for use in the present invention isalso more desirably an ion exchange resin possessing a chemicalstructure containing linking units represented by Chemical Formula 2Aand linking units represented by Chemical Formula 2B at a ratio ChemicalFormula 2A:Chemical Formula 2B=n:m, respectively, wherein both Ar₁ andAr₃ are linking units having a chemical structure of Chemical Formula 7,Ar₂ is a linking unit of a chemical structure represented by ChemicalFormula 3, and n and m are integers within a range of 1 to 1000 whichsatisfy Mathematical Expression 3.0.3≦n/(n+m)≦0.7  (Mathematical Expression 3)

When n/(n+m) in Mathematical Expressions 1 to 3 gets larger, the ionconductivity increases. At the same time the swellability by water alsoincreases and this will make the form stability of membranes tend to beaffected. On the other hand, when n/(n+m) in Mathematical Expressions 1to 3 gets smaller, the ion conductivity decreases. However, thepermeability of methanol tends to decrease. For solid polymer fuel cellsusing hydrogen as fuel, suitable are membranes which have a largen/(n+m) and also exert a high ion conductivity. For direct methanol-typefuel cells using methanol as fuel, membranes which have a small n/(n+m)and which exert less swellability by water and less methanolpermeability are suitable because methanol is normally used in the formof aqueous solution.

When used as a solid polymer electrolyte membrane in a solid polymerfuel cell using hydrogen as fuel, the ion exchange resin for use in thepresent invention is more desirably an ion exchange resin possessing achemical structure containing linking units represented by ChemicalFormula 2A and linking units represented by Chemical Formula 2B at aratio Chemical Formula 2A:Chemical Formula 2B=n:m, respectively, whereinboth Ar₁ and Ar₃ are linking units having a chemical structure ofChemical Formula 6, Ar₂ is a linking unit of a chemical structurerepresented by Chemical Formula 3, and n and m are integers within arange of 1 to 1000 which satisfy Mathematical Expression 4.0.5≦n/(n+m)≦0.7  (Mathematical Expression 4)

When used as a solid polymer electrolyte membrane in a solid polymerfuel cell using hydrogen as fuel, the ion exchange resin for use in thepresent invention is more desirably an ion exchange resin possessing achemical structure containing linking units represented by ChemicalFormula 2A and linking units represented by Chemical Formula 2B at aratio Chemical Formula 2A:Chemical Formula 2B=n:m, respectively, whereinboth Ar₁ and Ar₃ are linking units having a chemical structurerepresented by Chemical Formula 6, Ar₂ is a linking unit of a chemicalstructure represented by Chemical Formula 4, and n and m are integerswithin a range of 1 to 1000 which satisfy Mathematical Expression 5.0.4≦n/(n+m)≦0.8  (Mathematical Expression 5)

In addition, the ion exchange resin for use in the present invention isalso more desirably an ion exchange resin possessing a chemicalstructure containing linking units represented by Chemical Formula 2Aand linking units represented by Chemical Formula 2B at a ratio ChemicalFormula 2A:Chemical Formula 2B=n:m, respectively, wherein both Ar₁ andAr₃ are linking units having a chemical structure of Chemical Formula 7,Ar₂ is a linking unit of a chemical structure represented by ChemicalFormula 3, and n and m are integers within a range of 1 to 1000 whichsatisfy Mathematical Expression 6.0.4≦n/(n+m)≦0.6  (Mathematical Expression 6)

When used as a solid polymer electrolyte membrane in a direct methanolfuel cell using methanol as fuel, the ion exchange resin for use in thepresent invention is more desirably an ion exchange resin possessing achemical structure containing linking units represented by ChemicalFormula 2A and linking units represented by Chemical Formula 2B at aratio Chemical Formula 2A:Chemical Formula 2B=n:m, respectively, whereinboth Ar₁ and Ar₃ are linking units having a chemical structure ofChemical Formula 6, Ar₂ is a linking unit of a chemical structurerepresented by Chemical Formula 3, and n and m are integers within arange of 1 to 1000 which satisfy Mathematical Expression 7.0.2≦n/(n+m)≦0.5  (Mathematical Expression 7)

When used as a solid polymer electrolyte membrane in a direct methanolfuel cell using methanol as fuel, the ion exchange resin for use in thepresent invention is more desirably an ion exchange resin possessing achemical structure containing linking units represented by ChemicalFormula 2A and linking units represented by Chemical Formula 2B at aratio Chemical Formula 2A:Chemical Formula 2B=n:m, respectively, whereinboth Ar₁ and Ar₃ are linking units having a chemical structurerepresented by Chemical Formula 6, Ar₂ is a linking unit of a chemicalstructure represented by Chemical Formula 4, and n and m are integerswithin a range of 1 to 1000 which satisfy Mathematical Expression 8.0.2≦n/(n+m)≦0.5  (Mathematical Expression 8)

When used as a solid polymer electrolyte membrane in a direct methanolfuel cell using methanol as fuel, the ion exchange resin for use in thepresent invention is more desirably an ion exchange resin possessing achemical structure containing linking units represented by ChemicalFormula 2A and linking units represented by Chemical Formula 2B at aratio Chemical Formula 2A:Chemical Formula 2B=n:m, respectively, whereinboth Ar₁ and Ar₃ are linking units having a chemical structurerepresented by Chemical Formula 7, Ar₂ is a linking unit of a chemicalstructure represented by Chemical Formula 3, and n and m are integerswithin a range of 1 to 1000 which satisfy Mathematical Expression 9.0.3≦n/(n+m)≦0.5  (Mathematical Expression 9)

In a fuel cell, the ion exchange membrane is swollen by water containedin humidified fuel gas or oxidized gas or by water formed in thereaction if the fuel cell is a solid polymer fuel cell, or by water inan aqueous methanol solution supplied as fuel if the fuel cell is adirect methanol fuel cell. It is undesirable that the ion exchangemembrane be of great swellability because it may result in a highprobability of breakage of the membrane or delamination of electrodes.Among the above-described desirable structures of the ion exchangemembrane of the present invention, the structure in which Ar₁ and Ar₃are each a linking unit of the chemical structure represented byChemical Formula 6 and Ar₂ is a linking unit of the chemical structurerepresented by Chemical Formula 4 is a particularly desirable structurebecause the resin of such a structure is less swollen by water. Inparticular, one in which n and m satisfy Mathematical Expression 5 issuitable as an ion exchange membrane of a solid polymer fuel cell,whereas one in which n and m satisfy Mathematical Expression 8 issuitable as an ion exchange membrane of a direct methanol pattern fuelcell.

<Ionizable Group and Crosslinkable Group>

The ion exchange resin composition in the present invention desirablycontains a crosslinked ion exchange resin obtained by crosslinking anion exchange resin having an ionizable group in the molecule and alsohaving a photocrosslinkable group and/or a thermally crosslinkable groupin the molecule. In the present specification, when an ion exchangeresin has an ionic group in the molecule and also has aphotocrosslinkable group and/or a thermally crosslinkable group in themolecule, the ion exchange resin which is still in an uncrosslinkedstate is referred to as an “uncrosslinked ion exchange resin.”

The ionizable group which the uncrosslinked ion exchange resin has inthe molecule is not particularly restricted, but it is desirably, forexample, a sulfonic acid group, a phosphonic acid group, a phosphoricacid group, a carboxylic acid group or their salts with alkali metal orthe like. In the present specification, the ionizable group means agroup which can be dissociated to form an ion. Here, the ion exchangeresin composition of the present invention essentially contains anionizable group because the composition uses a monomer essentiallyhaving a sulfonic acid group (Chemical Formula 1) or a linking unit(Chemical Formula 2A). The ion exchange resin composition in the presentinvention may further have an ionizable group selected from thosementioned above. For example, if it further has a sulfonic acid group,its ion conductivity will increase more. Alternatively, if it has aphosphonic acid group, it will have an advantage that it can exert ionconductivity even at high temperatures.

The average content of ionizable groups in the uncrosslinked ionexchange resin is desirably not less than 0.1 mmol/g, and more desirablynot less than 1.0 mmol/g. In addition, the average content of ionizablegroups is desirably not more than 5.0 mmol/g, and more desirably notmore than 4.0 mmol/g. If the average content of ionizable groups is lessthan 0.1 mmol/g, the ion conductivity tends to fall greatly, whereas ifthe average content of ionizable groups is over 5.0 mmol/g, the membranetends to have a swellability as great as being able to be inhibited bycrosslinking.

The crosslinkable group that the uncrosslinked ion exchange resin foruse in the present invention has must be a crosslinkable reactive groupsuch as a thermally crosslinkable group and/or a photocrosslinkablegroup. The crosslinkable group the uncrosslinked ion exchange resin foruse in the present invention, which must contain at least a thermallycrosslinkable group or a photocrosslinkable group, may contain othercrosslinkable reactive group. Here, in the present specification, thethermally crosslinkable group means a group possessing a property ofcrosslinking when being heated. In the present specification, thephotocrosslinkable group means a group possessing a property ofcrosslinking when being irradiated with light. Further, in the presentspecification, the crosslinkable group is a term with a concept whichencompasses thermally crosslinkable groups and photocrosslinkable groupsand also encompasses other crosslinkable reactive groups.

The average content of such crosslinkable groups in the uncrosslinkedresin for use in the present invention is desirably one group permolecule or more, and more desirably 1 mmol/kg or more. The averagecontent is desirably 5,000 mmol/kg or less, and more desirably 500mmol/kg or less. If the average content of the crosslinkable group isless than one group per molecule, the swell-inhibiting effect bycrosslinking tend to become extremely slight. If the average content ofthe crosslinkable group is over 5,000 mmol/kg, the ion conductivitytends to decrease or it tends to become difficult to handle the membraneafter crosslinking due to loss of its flexibility.

It is possible to crosslink such crosslinkable groups by treating themby methods depending on their reactivities. It is possible to crosslinkthermally crosslinkable groups by heating treatment. It is also possibleto crosslink photocrosslinkable groups by light irradiation treatment.

<Thermally Crosslinkable Group>

The thermally crosslinkable group which the uncrosslinked ion exchangeresin for use in the present invention desirably has may be, but is notparticularly limited to, multiple bond groups such as an ethylene groupand an ethynyl group, benzoxazine group and an oxazole group.

Further, these groups may have a substituent such as a methyl group anda phenyl group. Such a thermally crosslinkable group may be present in amain chain of the uncrosslinked ion exchange resin for use in thepresent invention or alternatively may be present as a side chain. It isparticularly desirable that it be present as a terminal group of theuncrosslinked ion exchange resin.

Here, it is possible to introduce such a thermally crosslinkable groupinto the uncrosslinked ion exchange resin for use in the presentinvention by mixing starting monomers having a chemical structurepossessing the thermally crosslinkable group with starting monomershaving a chemical structure possessing no thermally crosslinkable groupand making them undergo a polymerization reaction as starting monomerswhich act as copolymerization monomers or terminators.

The average content of the thermally crosslinkable group in theuncrosslinked ion exchange resin for use in the present invention isdesirably 1 mmol/kg or more, and more desirably 5 mmol/kg or more. Theaverage content of the thermally crosslinkable group is desirably 1,000mmol/kg or less, and more desirably 500 mmol/kg or less. If the averagecontent of the thermally crosslinkable group is less than 1 mmol/kg, theswell-inhibiting effect by crosslinking tends to be extremely slight. Ifthe average content of the thermally crosslinkable group exceeds 1,000mmol/kg, it tends to become difficult to form a membrane due to theincrease in molecular weight of the uncrosslinked ion exchange resin.

Crosslinking of the thermally crosslinkable group which theuncrosslinked ion exchange resin for use in the present invention hascan be conducted by execution of heat treatment. It is desirable thatthe heat treatment be conducted under an atmosphere of an inert gas suchas nitrogen and argon.

The temperature of the heat treatment is desirably not lower than 100°C. and more desirably not lower than 200° C. Further, the temperature ofthe heat treatment is desirably not higher than 400° C., and moredesirably not higher than 300° C. If the temperature of the heattreatment is lower than 100° C., the crosslinking reaction tends not toproceed sufficiently. If the temperature of the heat treatment is over400° C., there is a tendency that thermal decomposition of the ionexchange resin itself readily occurs.

Further, the time of the heat treatment is desirably not shorter than 1second, more desirably not shorter than 60 seconds. The time of the heattreatment is desirably not longer than 100 hours, and more desirably notlonger than 30 hours. If the time of the heat treatment is shorter than1 second, heat does not transfer fully inside the membrane and thereforethe crosslinking reaction tends to occur nonuniformly. If the time ofthe heat treatment is over 100 hours, there is a tendency thatdecomposition or change in properties of the ion exchange resin itselfreadily occurs.

In addition, when conducting the heat treatment, it is permitted to addany known polymerization initiator such as azo-type polymerizationinitiators and peroxide-type polymerization initiators to the resincomposition containing the uncrosslinked ion exchange resin.

It is desirable that the thermally crosslinkable group which theuncrosslinked ion exchange resin for use in the present invention be atleast one thermally crosslinkable group selected from the groupconsisting of thermally crosslinkable groups of chemical structuresrepresented by Chemical Formulas 10 to 15.

(In Chemical Formulas 10 to 15, R¹ to R⁹ each independently represent ahydrogen atom, an alkyl group with a carbon number within a range of 1to 10, a phenyl group, an aromatic group with a carbon number within arange of 6 to 20 or a halogen atom; P represents a hydrogen atom, ahydrocarbon group with a carbon number within a range of 1 to 10,halogen, a nitro group or a —SO₃T group; T represents a H atom or amonovalent metal ion; o represents an integer within a range of 1 to 4).

Note that although these thermally crosslinkable groups may be of only asingle kind, two or more kinds of thermally crosslinkable groups mayalso be present together in the molecules of the same uncrosslinked ionexchange resin.

<Photocrosslinkable Group>

The thermally crosslinkable group which the uncrosslinked ion exchangeresin for use in the present invention has is not particularlyrestricted and examples thereof include a benzophenone group, anα-diketone group, an acyloin group, an acyloin ether group, a benzylalkyl ketal group, an acetophenone group, a group comprising apolynuclear quinone, a thioxanthone group and an acyl phosphine group.

Among such photocrosslinkable groups, it is particularly desirable touse, in combination, a group capable of generating a radical by theaction of light, such as a benzophenone group, and a group capable ofreacting with a radical, such as an aromatic group having a saturatedhydrocarbon group, e.g., a methyl group and an ethyl group, and anethylenically unsaturated group.

Depending on the skeleton structure of the uncrosslinked ion exchangeresin, in some cases, a crosslinking reaction will occur even thoughonly a group capable of generating a radical by the action of light,e.g., a benzophenone group, is present. In such cases, the group capableof react with a radical is not necessary and the uncrosslinked ionexchange resin for use in the present invention may have only aradical-generating group.

Such a photocrosslinkable group may be present in a main chain of theuncrosslinked ion exchange resin for use in the present invention oralternatively may be present as a side chain. It is particularlydesirable that it be present as a terminal group of the uncrosslinkedion exchange resin.

Here, it is possible to introduce such a photocrosslinkable group intothe uncrosslinked ion exchange resin for use in the present invention bymixing starting monomers having a chemical structure possessing thephotocrosslinkable group with starting monomers having a chemicalstructure possessing no photocrosslinkable group and making them undergoa polymerization reaction as starting monomers which act ascopolymerization monomers or terminators.

The average content of the photocrosslinkable group in the uncrosslinkedion exchange resin for use in the present invention is desirably 1mmol/kg or more, and more desirably 5 mmol/kg or more. The averagecontent of the photocrosslinkable group is desirably 5,000 mmol/kg orless, and more desirably 500 mmol/kg or less.

If the average content of the photocrosslinkable group is less than 1mmol/kg, the swell-inhibiting effect by crosslinking tend to becomeextremely slight. If the average content of the photocrosslinkable groupis over 5,000 mmol/kg, the ion conductivity tends to decrease or ittends to become difficult to handle the membrane after crosslinking dueto loss of its flexibility.

Crosslinking of the photocrosslinkable group which the uncrosslinked ionexchange resin for use in the present invention has can be conducted byexecution of light irradiation treatment. It is desirable that the lightirradiation treatment be conducted under an atmosphere of an inert gassuch as nitrogen and argon.

The temperature of the light irradiation treatment is desirably notlower than room temperature (25° C.) and more desirably not lower than50° C. Further, the temperature of the light irradiation treatment isdesirably not higher than 250° C., and more desirably not higher than200° C. If the temperature in the light irradiation treatment is lowerthan room temperature (25° C.), the crosslinking reaction tends to bedifficult to proceed. If the temperature in the light irradiationtreatment is higher than 250° C., side reactions such as decompositiontend to become easy to occur.

Further, the time of the light irradiation treatment is desirably notshorter than 1 second, more desirably not shorter than 30 seconds. Thetime of the light irradiation treatment is desirably not longer than 100hours, and more desirably not longer than 30 hours. If the time of thelight irradiation treatment is shorter than 1 second, the degree ofprogression of the crosslinking reaction tends to become inhomogeneousin the surface direction of the membrane. If the time of the lightirradiation treatment is longer than 100 hours, side reactions such asdecomposition and degradation tend to become easy to occur.

Here, it is desirable that the photocrosslinkable group which theuncrosslinked ion exchange resin for use in the present invention hascontain both a crosslinkable group having a chemical structurerepresented by Chemical Formula 8 and a crosslinkable group having achemical structure represented by Chemical Formula 9.

(In Chemical Formula 8 and Chemical Formula 9, R represents an aliphatichydrocarbon group with a carbon number within a range of 1 to 10 orepresents an integer within a range of 1 to 4).

The uncrosslinked ion exchange resin for use in the present inventiondesirably includes both the two types of photocrosslinkable groupshaving chemical structures represented by Chemical Formula 8 andChemical Formula 9.

<Other Reactive Groups Having Crosslinkability>

Other reactive groups having crosslinkability which the uncrosslinkedion exchange resin for use in the present invention has are notparticularly restricted. Examples thereof include an amino group, anepoxy group, a hydroxyl group, a halogen group, a halomethyl group and acarboxyl group.

<Introduction of Crosslinkable Group into Polymer Main Chain ofUncrosslinked Ion Exchange Resin>

In order to introduce a crosslinkable group into a polymer main chain ofthe uncrosslinked ion exchange resin for use in the present invention,it is desirable to use a specific compound which serves as a rawmaterial of the crosslinkable group. Such a compound may be added in thepolycondensation reaction system for obtaining a polymer main chain fromits beginning, or alternatively, it may be added in a stage when thepolycondensation reaction has already proceeded to some extent.

The compound to be used for introducing a thermally crosslinkable groupinto a polymer main chain of the uncrosslinked ion exchange resin foruse in the present invention is not particularly restricted. Examplesthereof include at least one compound selected from the group consistingof compounds having chemical structures represented by the followingChemical Formula 16A to Chemical Formula 16K.

Note that these compounds may be used either alone or as a mixture oftwo or more of them.

Among thermally crosslinkable groups introduced using these compounds, athermally crosslinkable group having a chemical structure represented byChemical Formula 10 is obtainable by making formaldehyde and amine reactto a polymer main chain having a phenolic hydroxyl group terminal asshown by Chemical Formula 17.

(In Chemical Formulas 17, R′ represents a hydrogen atom, an alkyl groupwith a carbon number within a range of 1 to 10, a phenyl group, anaromatic group with a carbon number within a range of 6 to 20 or ahalogen atom.

Note that these compounds may be used either alone or as a mixture oftwo or more of them.

The compound to be used for introducing a radical generating group,which is a kind of photocrosslinkable group, into a polymer main chainof the uncrosslinked ion exchange resin for use in the present inventionis not particularly restricted. Examples thereof include at least onecompound selected from the group consisting of compounds having chemicalstructures represented by the following Chemical Formula 18A to ChemicalFormula 18D.

Note that these compounds may be used either alone or as a mixture oftwo or more of them.

The compound to be used for introducing a group reactable with a radical(also referred to as a radical-reactable group in the presentspecification), which group is a kind of photocrosslinkable group, intoa polymer main chain of the uncrosslinked ion exchange resin for use inthe present invention is not particularly restricted. Examples thereofinclude at least one compound selected from the group consisting ofcompounds having chemical structures represented by the followingChemical Formula 19A to Chemical Formula 19F.

Note that these compounds may be used either alone or as a mixture oftwo or more of them.

In the uncrosslinked ion exchange resin for use in the present inventionhere, the radical generating group and the radical reactable group maybe present either in the same polymer main chain or in different polymermain chains.

As the uncrosslinked ion exchange resin for use in the presentinvention, two or more kinds of uncrosslinked ion exchange resins may beused in combination. Alternatively, an uncrosslinked ion exchange resinhaving both a radical-generating group and a radical-reactable group maybe used alone.

Specific examples of chemical structures of the uncrosslinked ionexchange resin for use in the present invention are represented by thefollowing Chemical Formula 20A to Chemical Formula 20I. Note thatchemical structures of the uncrosslinked ion exchange resin for use inthe present invention are not restricted to these chemical structures.

(In Chemical Formula 20A to Chemical Formula 20I, L represents a H atomor a monovalent metal ion. r and p each independently represent anypositive integer.)<Introduction of Ionizable Group into Polymer Main Chain ofUncrosslinked Ion Exchange Resin>

Although the ion exchange resin in the present invention essentially hasan ionizable group because it has a monomer or linking unit having asulfonic acid group as described above, an additional ionizable groupmay further be introduced into the polymer main chain of the ionexchange resin.

When further introducing an ionizable group into the uncrosslinked ionexchange resin, it is desirable to use a specific compound which isserved as a raw material of the ionizable group. Such a compound may beadded in the polycondensation reaction system for obtaining a polymermain chain from its beginning, or alternatively, it may be added in astage when the polycondensation reaction has already proceeded to someextent. It is also permitted to introduce an ionizable group into apolymer main chain in which the above-described crosslinkable groupalready has been introduced.

The compound to be used for introducing an ionizable group into apolymer main chain of the uncrosslinked ion exchange resin for use inthe present invention is not particularly restricted. For example, whenthe ionizable group is a sulfonic acid group, sulfonating agents such assulfuric anhydride, a complex of sulfuric anhydride, fuming sulfuricacid, concentrated sulfuric acid, chlorosulfonic acid may be used.

Here, in order to introduce an ionizable group into a polymer main chainin which a crosslinkable group already has been introduced, for example,a method may be used in which a molded article of polymer main chainshaving a crosslinkable group is treated with a sulfonating agent such assulfuric anhydride, sulfuric anhydride complex, fuming sulfuric acid,concentrated sulfuric acid and chlorosulfonic acid.

Alternatively, a method may also be used in which a sulfonating agent ismade react while a polymer main chain having a crosslinkable group isdissolved in a solvent which is inert to the sulfonating agent. Inaddition, a method may also be used in which a sulfonating agent is madereact while a polymer main chain having a crosslinkable group is swollenwith an appropriate solvent. Moreover, a method may also be used inwhich a polymer main chain having a crosslinkable group is made reactdirectly with a sulfonating agent.

Note that the sulfonating agent may be use as received or alternativelyit may be used while being dissolved or dispersed in an appropriatesolvent. The sulfonation reaction may be carried out in a gas phase or aliquid phase.

The temperature of the sulfonation reaction is desirably not lower than−100° C. and more desirably not lower than −30° C. Further, thetemperature of the sulfonation reaction is desirably not higher than100° C., and more desirably not higher than 80° C. If the temperature ofthe sulfonation reaction is lower than −100° C., it tends to becomedifficult to obtain a desired sulfonated product due to a great increasein viscosity of a solution or due to a decrease in reaction rate. If thetemperature of the sulfonation reaction temperature is over 100° C.,side reactions such as decomposition and crosslinking of polymers tendto become easy to occur.

The time of the sulfonation reaction is desirably not shorter than onehour, and more desirably not shorter than two hours. The time of thesulfonation reaction is desirably not longer than 100 hours, and moredesirably not longer than 80 hours. If the time of the sulfonationreaction is shorter than one hour, the sulfonation tends to occurnonuniformly or not to proceed sufficiently. If the time of thesulfonation reaction is over 100 hours, side reactions such asdecomposition and crosslinking of polymers tend to become easy to occur.

<Characteristics of Ion Exchange Resin>

The molecular weight of the ion exchange resin for use in the compositeion exchange membrane of the present invention (the resin is anuncrosslinked ion exchange resin when having an ionizable group in themolecule and having a photocrosslinkable group and/or a thermallycrosslinkable group) is desirably 1,000 or more, and more desirably5,000 or more. This molecular weight is preferably not more than1,000,000, and more preferably not more than 500,000 because physicalproperties and workability are well balanced. If the molecular weight isless than 1,000, it tends to become difficult to form a membrane or theswellability or water-solubility of the membrane tends to be high. Ifthe molecular weight is over 1,000,000, the viscosity of the solutionbecomes extremely high and therefore it tends to become difficult tohandle the solution.

Here, the degree of polymerization of the ion exchange resin for use inthe present invention can be expressed in inherent viscosity measured bythe method described below. That is, the inherent viscosity at 30° C. ofa 0.25 g/dl solution of the ion exchange resin for use in the presentinvention dissolved in N-methyl-2-pyrrolidone is desirably 0.1 or more,and more desirably 0.4 or more. The inherent viscosity is desirably notmore than 2.0, and more desirably not more than 1.5.

If the inherent viscosity is less than 0.1, it tends to become difficultto form a membrane or the swellability or water-solubility of themembrane tends to be high. If the inherent viscosity is over 2.0, theviscosity of the solution becomes extremely high and therefore it tendsto become difficult to handle the solution.

<Support Membrane>

The support membrane for use in the composite ion exchange membrane ofthe present invention must be a porous support membrane havingcontinuous pores penetrating through the membrane. This is because ifthe continuous pores penetrating through the membrane remain unfilledwith the ion exchange resin composition, it is impossible to obtain asatisfactory ion conductivity.

The porosity of the support membrane of the present invention isdesirably 90% by volume or more, and more desirably 95% by volume ormore. The porosity, which, as a matter of course, is not greater than100% by volume, is desirably 99% by volume or less. If the porosity isless than 95% by volume, the content of the ion exchange resin containedin the composite ion exchange membrane of the present invention achievedwhen the support membrane is impregnated with the ion exchange resincomposition will become small and therefore the ion conductivity tendsto decrease. If the porosity is over 99% by volume, the strength of thesupport membrane or the composite membrane tends to decrease.

It is desirable that the aperture ratio of at least one surface of thesupport membrane of the present invention be 40% or more, particularlydesirably 50% or more, and most desirably 60% or more. The apertureratio, which, as a matter of course, is not greater than 100%, isdesirably 95% or less. If the aperture ratio is less than 40%, whenmaking an ion exchange resin penetrate into a support membrane, itbecomes difficult to make the ion exchange resin penetrate inside poresof the support membrane. Therefore, the ion conductivity may decrease.If the aperture ratio is over 95%, the strength of a support membrane ora composite membrane tends to decrease.

The material for forming the support for use in the present invention isnot particularly restricted. Examples thereof include porous polyolefinresin films containing polymers such as polyethylene and polypropylene,porous fluorine-containing resin films containing polymers such aspolytetrafluoroethylene, porous polyimide resin films containingpolyimide polymer, porous polyamide resin films containing polyamidepolymer, porous cellulosic resin films containing cellulosic polymer,and porous polybenzazole resin film containing polybenzazole polymer.Among these materials, the porous polybenzazole resin film containing apolybenzazole polymer is particularly preferred as the material forforming the support membrane used in the present invention because it issuperior in heat resistance and strength and it can be processed into athin film.

When the support membrane for use in the present invention is composedof a porous polybenzazole resin film containing a polybenzazole polymer,it is desirable that the support membrane for use in the presentinvention be a support membrane obtained by obtaining the membrane byforming an isotropic solution containing the polybenzazole polymer in acontent within a range of 0.5 to 2% by mass into a film-like shape andsolidifying the solution. The support membrane containing such apolybenzazole polymer as a material is obtained by washing a membraneobtained by forming a film from a solution containing the polybenzazolepolymer and solidifying the film by making it contact with a poorsolvent.

When the solution containing the polybenzazole polymer is a solutionexhibiting optical anisotropy, it, in some cases, is impossible toobtain a membrane containing, as its material, a porous polybenzazolepolymer having continuous pores with a porosity as large as the polymercan accept a large amount of ion exchange resin. It, therefore, isdesirable to use an isotropic solution as the solution containing thepolybenzazole polymer.

The polybenzazole polymer used as the support membrane in the presentinvention refers to polymers having a structure containing an oxazolering, a thiazole ring and an imidazole ring in the polymer chain andspecifically to polymers containing a repeating unit represented by thefollowing general formulas in the polymer chain.

Here, U₁, U₂ and U₃ each represent an aromatic unit, which may have asubstituent such as various types of aliphatic group, aromatic group,halogen group, hydroxyl group, nitro group, cyano group andtrifluoromethyl group. These aromatic units may be monocyclic units suchas benzene ring, condensed ring units such as naphthalene, anthraceneand pyrene, and polycyclic aromatic units in which such aromatic unitsare linked via two or more arbitrary bonds. The positions of N and X inaromatic units are not particularly restricted if a configuration suchthat a benzazole ring can be formed is established. Moreover, these maybe heterocyclic aromatic units containing N, O, S or the like inaromatic rings as well as hydrocarbon aromatic units. X represents O, Sand NH.

The aforementioned U₁ is desirably any of ones represented by thefollowing general formulas.

Here, T₁ and T₂ each represent CH or N, and T₃ represents a direct bond,—O—, —S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂— and —CO—.

The aforementioned T₂ is desirably any of ones which are represented bythe following general formulas.

Here, W represents —O—, —S—, —SO₂—, —C(CH₃)₂—, —C(CF₃)₂— and —CO—.

The aforementioned U₃ is desirably any of ones which are represented bythe following general formula.

These polybenzazole polymers may be homopolymers having the foregoingrepeating units. Alternatively, they also may be random, alternating orblock copolymers comprising a combination of the above-mentionedstructural units, examples of which include those disclosed in U.S.Unexamined Patent Publication No. 2002/0091225 specification, U.S. Pat.Nos. 4,703,103, 4,533,692, 4,533,724, 4,533,693, 4,539,567 and4,578,432.

The linking units contained in the polybenzazole polymer for use in thepresent invention are not particularly restricted, but are desirablyselected, for example, from linking units which are capable of forming alyotropic liquid crystal polymer.

Specific examples of such polybenzazole structural units containinglinking units capable of forming a lyotropic liquid crystal polymerinclude ones represented by the following structural formulas.

In addition, not only these polybenzazole structural units, but alsorandom, alternating or block copolymers with additional polymerstructural units are available. In such a situation, the additionalpolymer structural units are preferably chosen from aromatic polymerstructural units with superior heat resistance. Specific examplesinclude polyimide structural units, polyamide structural units,polyamideimide structural units, polyoxydiazole structural units,polyazomethine structural units, polybenzazoleimide structural units,polyetherketone structural units and polyethersulfone structural units.

Examples of the polyimide structural units include ones represented bythe following general formula.

Here, U₄ is represented by a tetravalent aromatic unit. Preferred arethose represented by the following structures.

U₅ is a divalent aromatic unit and preferred are those represented bythe following structures. On the aromatic rings shown here, variouskinds of substituents may be present such as a methyl group, a methoxygroup, a halogen group, a trifluoromethyl group, a hydroxyl group, anitro group and a cyano group.

Specific examples of these polyimide structural units include onesrepresented by the following structural formulas.

Examples of polyamide structural units include those represented by thefollowing structural formulas.

Here, U₆, U₇ and U₈ are preferably each independently one which isselected from the following structures. On the aromatic rings shownhere, various kinds of substituents may be present such as a methylgroup, a methoxy group, a halogen group, a trifluoromethyl group, ahydroxyl group, a nitro group and a cyano group.

Specific examples of these polyamide structural units include onesrepresented by the following structural formulas.

Examples of polyamideimide structural units include ones represented bythe following structural formulas.

Here, U₉ is desirably selected from the structures provided above asspecific examples of U₅.

Specific examples of these polyamideimide structural units include onesrepresented by the following structural formulas.

Examples of polyoxydiazole structural units include ones represented bythe following structural formulas.

Here, U₁₀ is desirably selected from the structures provided above asspecific examples of U₅.

Specific examples of such polyoxydiazole structural units include onesrepresented by the following structural formulas.

Examples of polyazomethine structural units include ones represented bythe following structural formulas.

Here, U₁₁ and U₁₂ are desirably selected from the structures providedabove as specific examples of U₆.

Specific examples of these polyazomethine structural units include onesrepresented by the following structural formulas.

Examples of polybenzazoleimide structural units include ones representedby the following structural formulas.

Here, U₁₃ and U₁₄ are desirably selected from the structures providedabove as specific examples of U₄.

Specific examples of such polybenzazoleimide structural units includeones represented by the following structural formulas.

Polyetherketone structural units and polyethersulfone structural unitsare structural units generally having a structure in which aromaticunits are combined via a ketone bond or a sulfone bond as well as anether bond, which include structural components selected from thefollowing structural formulas.

Here, U₁₅ to U₂₃ are desirably each independently ones represented bythe following structures. On the aromatic rings shown here, variouskinds of substituents may be present such as a methyl group, a methoxygroup, a halogen group, a trifluoromethyl group, a hydroxyl group, anitro group and a cyano group.

Specific examples of these polyetherketone structural units include onesrepresented by the following structural formulas.

The aromatic polymer structural units which can be copolymerizedtogether with these polybenzazole polymer structural units do not referexactly to repeating units in polymer chains, but refer to structuralunits which can be present in polymer chains together with polybenzazolestructural units. With respect to these copolymerizable aromatic polymerstructural units, not only a single kind of units but also two or morekinds of units may be copolymerized in combination. Such copolymers canbe synthesized by introducing amino groups, carboxyl groups, hydroxylgroups, halogen groups or the like at unit terminals formed ofpolybenzazole polymer structural units, followed by polymerizing theresultant as reaction components in the synthesis of those aromaticpolymers, or introducing carboxyl groups at unit terminals of thosearomatic polymer structural units, followed by polymerizing theresultant as reaction components in the synthesis of polybenzazolepolymer.

Here, the polybenzazole polymer for use in the present invention isobtained by subjecting linking units such as those described above tocondensation polymerization in a polyphosphoric acid solvent.

The degree of polymerization of the polybenzazole polymer for use in thepresent invention is expressed in intrinsic viscosity. The intrinsicviscosity is desirably 15 dl/g or higher, and more desirably 20 dl/g orhigher. The intrinsic viscosity is desirably 35 dl/g or lower, and moredesirably 26 dl/g or lower.

If the intrinsic viscosity is lower than 15 dL/g, the strength of thesupport membrane obtained by use of the polybenzazole polymer as amaterial tends to decrease. If the intrinsic viscosity is higher than 35dL/g, the concentration range of the polybenzazole polymer in apolybenzazole polymer solution from which an isotropic solution isobtained is limited and, in some cases, it becomes difficult to preparea support membrane under isotropic conditions.

As the method for forming a support membrane from a solution containingthe polybenzazole polymer for use in the present invention, all themethods by which the polymer solution is formed into a film-like shapemay be used, for example, in addition to a film forming method calledthe casting method in which a polymer solution is cast on a substrateusing a doctor blade or the like, a method comprising extruding thepolymer solution through a linear slit die, a method comprising blowextruding the polymer solution through a circular slit die, a sandwichmethod comprising pressing the polymer solution sandwiched between twosubstrates through a roller, and spin coating.

Among these film forming methods, particularly desirable methodssuitable for the purpose of the support membrane for use in the presentinvention are the casting method and the sandwich method. As a substrateplate for the casting method or a substrate for the sandwich method,glass plates, metal plates, resin films and the like can be used. Inaddition, for the purpose of controlling the pore structure of a supportmembrane at solidification, various types of porous material can bepreferably employed as a substrate plate or substrate.

In order to obtain a support membrane which is uniform and has a highporosity, it is important to form the solution of the polybenzazolepolymer for use in the present invention into a support membrane in acomposition of isotropic conditions.

Therefore, the concentration of the polybenzazole polymer in thepolybenzazole polymer solution for use in the present invention isdesirably 0.5% or higher, and more desirably 0.8% or higher. Further,the concentration is desirably 2% or lower, and more desirably 1.5% orlower. If the concentration is lower than 0.5%, the polymer solutioncomes to have a low viscosity and therefore film forming methods whichcan be applied are restricted and, in some cases, resulting supportmembranes come to have a reduced strength. If the concentration is over2%, it may be difficult to obtain a support membrane with a highporosity or, depending on the polymer composition or degree ofpolymerization of the polybenzazole polymer, the solution of thepolybenzazole polymer may exhibit anisotropic properties.

In order to adjust the concentration of the polybenzazole polymersolution for use in the present invention within the above range,methods shown below may be employed. One specific example is a methodwhich comprises separating a solid of polybenzazole polymer temporarilyfrom a polybenzazole polymer solution obtained by a polymerizationreaction and then adding a solvent again to dissolve the solid, therebyadjusting the concentration.

Another example is a method which comprises adding a solvent to asolution of polybenzazole polymer obtained by a condensationpolymerization reaction conducted in polyphosphoric acid withoutseparating a solid of the polybenzazole polymer from the solution asreceived, thereby diluting the solution to adjust its concentration.Still another example is a method comprising directly obtaining apolybenzazole polymer solution having a concentration range mentionedabove by adjusting the polymerization composition of the polybenzazolepolymer.

Examples of solvents suitably used for adjusting the concentration ofthe solution of the polybenzazole polymer for use in the presentinvention include methanesulfonic acid, dimethylsulfuric acid,polyphosphoric acid, sulfuric acid and trifluoroacetic acid. Mixedsolvents comprising combinations of these solvents may also be used.Among these solvents, methanesulfonic acid and polyphosphoric acid areparticularly preferred.

As a method for realizing the porous structure of the support membranefor use in the present invention, a method is used which comprisescontacting an isotropic polybenzazole polymer solution in a film formwith a poor solvent to solidify it. The poor solvent is desirably asolvent which is miscible with the solvent of the polybenzazole polymersolution. The poor solvent may be either in a liquid phase state or in agas phase state. In addition, a method comprising a combination ofsolidification using a poor solvent in a gas phase state andsolidification using a poor solvent in a liquid phase state can also beemployed suitably.

Here, as the poor solvent to be used for the solidification, water,aqueous solutions of acids, aqueous solutions of inorganic salts,organic solvents such as alcohol, glycol and glycerin, and so on may beused. Particular caution is required in choice of the poor solvent usedfor the solidification because in some combinations with thepolybenzazole polymer solution to be used, problems will arise, forexample, the support membrane comes to have a small surface apertureratio or a small porosity, or discontinuous voids are formed inside thesupport membrane.

In the solidification of an isotropic polybenzazole polymer solution inthe present invention, the structures and the porosities of the surfaceand the inside of the support membrane are controlled successfully bychoosing a poor solvent among water vapor, aqueous solution ofmethanesulfonic acid, aqueous solution of phosphoric acid, aqueoussolution of glycerin and aqueous solutions of inorganic salts such asaqueous solution of magnesium chloride and further by choosingsolidification conditions.

Among these methods, particularly preferred methods for solidificationinclude a method comprising contacting the solution with water vapor tosolidify it, a method comprising contacting the solution with watervapor for a short period of time in the early stage of solidificationand then contacting it with water, and a method comprising contactingthe solution with an aqueous solution of methanesulfonic acid.

The support membrane tends to shrink with progress of solidification ofthe solution of the polybenzazole polymer. Therefore, during theprogress of the solidification, a tenter or a fixing frame may be usedfor inhibiting the formation of wrinkles caused by uneven shrinkage ofthe support membrane. Moreover, in the case of solidifying apolybenzazole polymer solution shaped on a substrate plate such as aglass plate, the shrinkage on the substrate plate may be inhibited bycontrolling the roughness of the surface of the substrate plate.

It is desirable that the support membrane solidified in the mannermentioned above be fully washed for avoidance of problems such asacceleration of decomposition of the polybenzazole polymer caused byremaining solvent and spill of remaining solvent during the use of thesupport membrane as a material of a composite ion exchange membrane. Thewashing can be performed through immersion of the support membrane inwashing liquid. Particularly desirable washing liquid is water. It isdesirable that the washing with water be carried out until the washingscome to have a pH within a range of 5 to 8, more desirably from 6.5 to7.5 when the support membrane is immersed in water.

By use of an isotropic polybenzazole polymer solution having aconcentration within the above-mentioned specific range and use of anappropriate solidification method selected from the methods mentionedabove, a support membrane can be obtained which is made of apolybenzazole polymer having a structure most suitable for the purposeof the support membrane for use in the present invention. It is a poroussupport membrane which has continuous voids having openings in at leastone surface of the support membrane at an appropriate aperture ratio.This support membrane has three-dimensional network structure made offibril-like fibers of polybenzazole polymer and has three-dimensionallycontinuous voids. The structure of such a support membrane can beconfirmed through an observation of the surface of the support membranein water using an atomic force microscope and through a cross-sectionalobservation using transmission electron microscopic observation of thesupport membrane holding its structure in water by epoxy embedding-epoxyremoval.

The support membrane in the present invention desirably has a porosityof 90% or more, and more desirably 95% or more. A porosity under thisrange is undesirable because combining of the membrane with ion exchangeresin results in a small content of the ion exchange resin, which leadsto a reduced ionic conductivity.

The support membrane of the present invention has openings in bothsurfaces thereof. At least one surface desirably has an aperture ratioof 40% or more, more desirably 50% or more, and particularly desirably60% or more. It is undesirable that at least one surface has an apertureratio less than such ranges because, if so, the adhesion between thelayer of the support membrane impregnated with the ion exchange resinand the layers of the ion exchange resin formed on both surfaces of thesupport membrane falls and therefore the ion conductivity falls. Inaddition, the ion exchange resin layers will become liable todelaminate.

<Production Method of Composite Ion Exchange Membrane>

Described below is a method for obtaining a composite ion exchangemembrane by impregnating a porous support membrane made of polybenzazolepolymer obtained by the method described above with an ion exchangeresin composition.

A description is made to a method which includes immersing the supportmembrane in a solution containing the ion exchange resin compositionwithout drying the membrane to allow the solution containing the ionexchange resin composition to displace the liquid inside the supportmembrane and then conducting drying, thereby obtaining a composite ionexchange membrane.

When the liquid inside the ion exchange membrane has a solventcomposition different from that of the solution containing the ionexchange resin, a method which includes allowing the liquid inside themembrane to be displaced in advance in conformity to the solventcomposition of the solution may also be applied.

The porous support membrane obtained from an isotropic polybenzazolepolymer solution has a characteristic in that the apparent volume of thesupport membrane decreases greatly as the volume of the liquid insidethe voids of the support membrane is reduced through drying because thevoid structure shrinks with the liquid volume reduction.

Therefore, in the case of drying the support membrane while controllingits shrinkage in its surface direction by fixing it in a metal framewithout allowing no ion exchange resin composition to penetrate into thesupport membrane, it is normal that shrinkage occurs in the thicknessdirection and the apparent thickness of the support membrane after thedrying is within a range of 0.5% to 10% of the thickness before thedrying.

Porous support membranes other than the support membrane for use in thepresent invention, for example, support membranes composed of porousmembranes made of drawn polytetrafluoroethylene polymer do not sufferfrom such a great shrinkage.

Because of such a characteristic of the support membrane for use in thepresent invention, when the liquid inside the voids of the supportmembrane is displaced by a solution containing an ion exchange resincomposition and then the solution is dried, the support membrane shrinksas the volume of the solution containing the ion exchange resincomposition decreases through evaporation of the solvent of the solutioncontaining the ion exchange resin composition contained in the voids.Therefore, it is possible to obtain easily a dense composite ionexchange membrane structure where the voids in the support membrane arefilled with the crystallized ion exchange resin composition. Because ofthe composite ion exchange membrane structure, the composite ionexchange membrane of the present invention exhibits excellentdimensional stability, mechanical strength and fuel permeationinhibitability.

The solvent in the solution containing an ion exchange resin describedabove may be selected from solvents which can dissolve the ion exchangeresin composition without dissolving, decomposing or extremely swellinga support membrane made of a polybenzazole polymer.

In order to impregnate the support membrane with the solution containingan ion exchange resin and then precipitate the ion exchange resin byremoving the solvent, it is desirable that the solvent be one which canbe removed, for example, by being evaporated by means of heating orpressure reduction.

Examples of such solvents include highly polar solvents such asN,N′-dimethylformamide, N,N′-dimethylacetamide, N-methyl-2-pyrrolidone,hexamethyl phosphonamide, dimethylsulfoxide and sulfolane, alcohols suchas methanol, ethanol, propanol and butanol, polar solvents such asacetone and methyl ethyl ketone, phenols such as creosol, water andtheir mixed solvents.

The support membrane for use in the present invention has a s high heatresistance when it is a support membrane made of a polybenzazolepolymer. Therefore, it is possible to produce composite ion exchangemembranes using a solution of an ion exchange resin compositioncontaining a high-boiling solvent which can not be used in thepreparation of known composite ion exchange membranes using supportmembranes made of polytetrafluoroethylene which exhibits creep at atemperatures of about 100° C. This fact shows that the support membranefor use in the present invention has a superior characteristic from theviewpoint that many kinds of ion exchange resin compositions can bechosen.

The concentration of the ion exchange resin in the solution of the ionexchange resin composition to be used in the present invention, which isnot particularly limited, is desirably not lower than 1% by mass, andmore desirably not lower than 10% by mass. Further, the concentration isdesirably not higher than 50% by mass, and more desirably not higherthan 40% by mass. If the concentration is lower than 1% by mass, thecontent of the ion exchange resin in the composite membrane tends tofall. If the concentration is over 50% by mass, there is a tendency thatthe rate of the composite layer in the composite membrane falls, whichdecreases the reinforcing effect, that the thickness of the compositemembrane becomes too great, which reduces the power generatingperformance, or that the ion exchange resin solution penetrates into thesupport membrane insufficiently, which facilitates the formation ofvoids in the composite membrane.

The content of the ion exchange resin in the composite ion exchangemembrane of the present invention is desirably not less than 50% bymass, and more desirably not less than 80% by mass. The content, whichas a matter of course is not greater than 100%, is desirably not morethan 99% by mass. The cases where the content is less than 50% by masstend to be undesirable because no sufficient power generationperformance is achieved due to a resulting high conduction resistance ofthe composite ion exchange membrane or a resulting low water retentivityof the composite ion exchange membrane. If the content is over 99% bymass, the strength or swelling resistance of the composite membranetends to fall.

The composite ion exchange membrane of the present invention desirablyis less inhomogeneous in content of the ion exchange resin inside themembrane. In other words, for a straight line running through thecomposite membrane along its thickness direction, when a linear analysisfor elements contained only in the ion exchange resin is conducted usingan electron probe microanalyzer, the variation in the number of X-rayscounted, as indicated in CV value, is desirably up to 50%, moredesirably up to 40%, and particularly desirably up to 25%. This isbecause if the variation in the number of X-rays counted is larger thanthe above, the content of the ion exchange resin inside the compositeion exchange membrane is inhomogeneous; the membrane has a reduced ionconductivity; moreover the composite membrane has a reduced mechanicalstrength; and therefore no sufficient power generation performance maybe achieved.

The composite ion exchange membrane of the present invention desirablyhas inside a region as less as possible where no ion exchange resin ispresent. In other words, when a linear analysis is conducted over ananalysis area spreading through the composite membrane along itsthickness direction by using an electron probe microanalyzer, the numberof analysis points where the number of the counted X-rays of theanalyzed elements is 5% or less relative to the maximum number among thevalues obtained at all the analysis points in the composite membrane isdesirably 0 to 30%, more preferably 0 to 20%, and even more desirably 0to 10% of the number of all the analysis points. If the number ofanalysis points where said number is not more than 5% of the maximumnumber is more than the above, no sufficient power generationperformance is obtained because the inside of the composite ion exchangemembrane has much region where no ion exchange resin is present, thatis, region which does not contribute to ion conductivity, which resultsin reduction in ion conductivity of the membrane.

<Structure of Composite Ion Exchange Membrane>

The thickness of the composite ion exchange membrane of the presentinvention is desirably not less than 10 μm, and more desirably not lessthan 20 μm. Further, this thickness is desirably not more than 500 μm,and more desirably not more than 100 μm. If the thickness is less than10 μm, a problem of causing a large fuel crossover easily occurs. If thethickness is over 500 μm, the conducting resistance of the composite ionexchange membrane tends to increase.

It is possible to control the thickness of the composite ion exchangemembrane of the present invention by adjusting the clearance or theconcentration of the polybenzazole polymer solution for forming thesupport membrane during the preparation of the support membrane or byadjusting the concentration of the solution containing the ion exchangeresin composition.

The composite ion exchange membrane of the present invention preferablyhas a surface layer comprising the ion exchange resin composition oneach side of the support membrane.

The composite ion exchange membrane of the present invention exhibitsbetter characteristics if it has, on both sides of a composite layer 2including both a support membrane and an ion exchange resin composition,surface layers 1, 3 composed of an ion exchange resin compositioncontaining no support membrane with the composite layer 2 sandwichedtherebetween as depicted in FIG. 1. This is because, by possessing sucha structure, the composite ion exchange membrane has superiorcharacteristics, namely, a high mechanical strength and a superioradhesion with an electrode layer when the electrode layer is formed on asurface thereof.

The thickness of the surface layers is desirably not less than 1 μm, andmore desirably not less than 2 μm. Further, this thickness is desirablynot more than 50 μm, and more desirably not more than 30 μm. Inaddition, the thickness is desirably not greater than half the overallthickness of the composite ion exchange membrane. If the thickness isless than 1 μm, the adhesion with the electrode layer falls, which mayresults in decrease in ion conductivity. If the thickness is over 50 μmor it is greater than half the overall thickness of the composite ionexchange membrane, the reinforcing effect caused by the composite layerdoes not reach the outermost layer of the composite ion exchangemembrane and therefore when the composite ion exchange membrane absorbsmoisture, only the surface layers swell greatly and they may delaminatefrom the composite layer.

In the composite ion exchange membrane of the present invention, amethod in which the composite ion exchange membrane is subjected to heattreatment under appropriate conditions may also be employed desirablyfor the purpose of further improving characteristics of the compositeion exchange membrane such as mechanical strength, ionic conductivityand delamination resistance of the crosslinked ion exchange resincomposition layers formed on the surfaces.

In the composite ion exchange membrane of the present invention, it isalso permitted to further immerse the composite ion exchange membraneinto a solution containing the ion exchange resin composition in orderto adjust the thickness of the surface layers of the ion exchange resincomposition to be formed on the surfaces of the membrane. Moreover, inthe composite ion exchange membrane of the present invention, it is alsopermitted to increase the amount of the adhered layers of the ionexchange resin composition by applying the solution containing the ionexchange resin composition to the composite ion exchange membrane andthen drying.

Alternatively, in the composite ion exchange membrane of the presentinvention, it is also permitted to use a method in which the amount ofthe adhered layers of the ion exchange resin composition is reduced by,after the immersion of the composite ion exchange membrane in thesolution containing the ion exchange resin composition, scraping offpart of the ion exchange resin composition adhered to the surface of thesupport membrane by using a scraper, an air knife or a roller orabsorbing the solution with a material with solution absorbability suchas filter paper and sponge.

Furthermore, in the composite ion exchange membrane, a method in whichthe adhesion of the ion exchange resin composition layer is furtherimproved by hot pressing is also used in combination.

The composite ion exchange membrane of the present invention, which hassuch a structure, is superior in mechanical strength while having a highionic conductivity. It is possible to use the composite ion exchangemembrane of the present invention as a solid polymer electrolytemembrane for solid polymer fuel cells by making the most of thecharacteristics of the membrane.

EXAMPLES

While the present invention is described in more detail in Examples, thepresent invention is not restricted to these.

<Synthesis of Ion Exchange Resin>

First, ion exchange resins to be used in Examples of the presentinvention and Comparative Examples were synthesize in the mannersdescribed in Synthesis Examples below.

(i) Synthesis Example 1

First, 12.28 g (25.0 mmol) of sodium4,4′-dichlorodiphenylsulphone-3,3′-disulfonate, 7.18 g (25.0 mmol) of4,4′-chlorodiphenylsulfone, 9.31 g (50.0 mmol) of 4,4′-biphenol, 7.95 g(57.5 mmol) of potassium carbonate, 100 ml of N-methyl-2-pyrrolidone and15 ml of toluene were charged into a 200 ml side-arm flask equipped witha nitrogen introduction tube, a stirring blade, a Dean-Stark trap and athermometer and then were heated under nitrogen flow while being stirredon an oil bath.

Subsequently, after dehydration by azeotropy with toluene was conductedat 140° C., toluene was removed completely by distillation. Thereafterthe temperature was raised to 200° C. and heating was continued for 15hours. Subsequently, the solution cooled to room temperature was pouredinto 2000 ml of pure water. Thus, ion exchange resin was reprecipitated.Then, the ion exchange resin filtered was dried under reduced pressureat 50° C. to yield the ion exchange resin of Synthesis Example 1.

(ii) Synthesis Examples 2 to 12

The ion exchange resins of Synthesis Examples 2 to 12 were synthesizedin the same manner as Example 1, with the exception that the kinds andmolar ratios of monomers were changed as shown in Table 1. The yieldsand the measurements of inherent viscosity of the ion exchange resin arealso shown in Table 1.

TABLE 1 Charge amount of monomer (mmol) Inherent S- Yield viscosityDCDPS DCBN DCDPS BP BPF (%) (dl/g) Synthesis 25 — 25 50 — 95 0.95Example 1 Synthesis 30 — 20 50 — 93 0.83 Example 2 Synthesis 35 — 15 50— 90 0.77 Example 3 Synthesis 25 — 25 — 50 91 0.54 Example 4 Synthesis35 — 15 — 50 89 0.53 Example 5 Synthesis 40 — 10 — 50 85 0.59 Example 6Synthesis 20 30 — 50 — 93 0.88 Example 7 Synthesis 25 25 — 50 — 91 0.91Example 8 Synthesis 30 20 — 50 — 84 0.79 Example 9 Synthesis 15 — 35 50— 97 0.94 Example 10 Synthesis 18 — 32 — 50 98 0.55 Example 11 Synthesis13 37 50 — 96 0.91 Example 12 S-DCDPS: sodium4,4′-dichlorodiphenylsulfone-3,3′-disulfonate DCBN:2,6-dichlorobenzonitrile DCDPS: 4,4′-dichlorodiphenylsulfone BP:4,4′-biphenol BPF: 9,9-bis(4-hydroxyphenyl)fluorene

(iii) Comparative Synthesis Example 1

First, 10 g of polyphenylsulfone (trade name: Polyphenylsulfone, made byAldrich Chemical Company, Inc.) was dissolved in 100 g of concentratedsulfuric acid. Subsequently, 4 ml (0.03 mol in terms of SO₃) of 30%fuming sulfuric acid was dropped and a reaction was carried out forthree hours in a cool water bath. Then, the reaction solution was pouredinto water to be subjected to reprecipitation, followed by washing withwater until no free acid was detected in washings by means of pH testpaper, filtration and drying under reduced pressure at 50° C. Thus, thesulfonated polyphenylsulfone of Comparative Synthesis Example 1 wasobtained. The yield was 90%.

Example 1

First, an isotropic solution with apoly(p-phenylene-cis-benzobisoxazole) concentration of 1% by mass wasprepared by diluting a dope comprising polyphosphoric acid containing14% by mass of poly(p-phenylene-cis-benzobisoxazole) polymer having anintrinsic viscosity of 25 dL/g by addition of methane sulfonic acid.

Then, this solution was formed into a film on a glass plate heated to90° C. at a film formation rate of 5 mm/sec using an applicator with aclearance of 300 μm. The dope film formed on the glass plate was placedas it was in a thermohygrostat at 25° C. and 80% RH and was solidifiedfor one hour. The resulting film was washed with water until thewashings exhibited pH 7±0.5, yielding a support membrane.

Subsequently, the surface morphology observation by an atomic forcemicroscope and the section morphology observation by a transmissionelectron microscope of the resulting support membrane confirmed that themembrane was a porous membrane with continuous pores having openings inboth surfaces of the membrane. As a result of the measurement byobservation, the support membrane had an aperture ratio of 69% and aporosity of 98%.

The support membrane was then fixed into a stainless frame in water andwas immersed in a 25% aqueous solution of dimethylacetamide (DMAc), a50% aqueous solution of DMAc and a 75% aqueous solution of DMAc in orderfor one hour each. Finally, the support membrane was immersed in DMAc,so that the solvent contained in the support membrane was changed fromwater to DMAc.

Then, a solution containing an ion exchange resin was prepared bystirring 10 g of the ion exchange resin produced by a polymerizationreaction in Synthesis Example 1 together with 40 g DMAc for three days.Subsequently, the support membrane was immersed in a solution containingan ion exchange resin at 25° C. for 15 hours and then was removed fromthe solution. The solvent in the solution which permeated into themembrane and attached to the surface of the membrane was volatilized todry by hot air.

The dried membrane was further dried under reduced pressure at 120° C.overnight. Thereafter, the membrane was treated with 1 mol/L sulfuricacid at 80° C. for one hour, so that the sulfonic group was converted tothe acid form. The membrane was washed further with water until no acidwas detected. Thus, the composite ion exchange membrane of Example 1 wasobtained.

Examples 2 to 12

The composite ion exchange membranes of Examples 2 to 12 were preparedin the same manner as Example 1 except that the ion exchange resinserved as a material of the composite ion exchange membrane was changedto the ion exchange resins of Synthesis Examples given in Table 2.

TABLE 2 Thickness (μm) ICP Ion Methanol Support Total Composite contentIEC conductivity Swellability permeation rate ICP membrane thicknesslayer (wt %) (meq/g) (S/cm) (%) (mmol · m⁻² · sec⁻¹) Example 1 SynthesisPBO 49 30 93 1.67 0.25 31 8.1 Example 1 Example 2 Synthesis PBO 44 28 931.92 0.30 38 10.7 Example 2 Example 3 Synthesis PBO 39 29 92 2.11 0.3740 13.1 Example 3 Example 4 Synthesis PBO 41 29 92 1.24 0.14 29 3.9Example 4 Example 5 Synthesis PBO 51 28 94 1.65 0.20 36 4.9 Example 5Example 6 Synthesis PBO 45 26 93 1.83 0.23 39 6.8 Example 6 Example 7Synthesis PBO 48 28 93 1.66 0.24 28 5.3 Example 7 Example 8 SynthesisPBO 48 30 93 1.89 0.31 35 7.1 Example 8 Example 9 Synthesis PBO 42 26 922.04 0.33 40 9.3 Example 9 Example 10 Synthesis PBO 41 25 92 1.15 0.0925 4.5 Example 10 Example 11 Synthesis PBO 38 26 91 0.99 0.07 20 3.2Example 11 Example 12 Synthesis PBO 40 27 92 1.02 0.06 21 3.3 Example 12Comparative Synthesis None 39 — 100 1.73 0.26 50 12.3 Example 1 Example1 Comparative Synthesis None 44 — 100 2.00 0.32 59 14.3 Example 2Example 2 Comparative Synthesis None 41 — 100 2.16 0.36 68 16.7 Example3 Example 3 Comparative Synthesis None 45 — 100 1.21 0.12 51 4.9 Example4 Example 4 Comparative Synthesis None 42 — 100 1.67 0.24 62 6.4 Example5 Example 5 Comparative Synthesis None 45 — 100 1.91 0.27 69 9.5 Example6 Example 6 Comparative Synthesis None 49 — 100 1.62 0.24 48 6.3 Example7 Example 7 Comparative Synthesis None 50 — 100 1.95 0.29 58 9.1 Example8 Example 8 Comparative Synthesis None 42 — 100 2.14 0.35 74 12.8Example 9 Example 9 Comparative Synthesis None 39 — 100 1.21 0.11 32 6.1Example 10 Example 10 Comparative Synthesis None 38 — 100 1.05 0.09 275.5 Example 11 Example 11 Comparative Synthesis None 40 — 100 1.09 0.0726 5.3 Example 12 Example 12 Comparative Comparative PBO 35 9 84 1.650.09 33 7.1 Example 13 Synthesis Example 1 ICP: Ion exchange resin (Ionexchange plastic) IEC: Ion exchange capacity

Comparative Example 1

In Comparative Example 1, in contrast to Examples 1 to 12, the ionexchange resin synthesized in Synthesis Example 1 was formed alone intoa film without being fabricated into a composite membrane.

First, a solution prepared by dissolving 0.8 g of the ion exchange resinof Synthesis Example 1 in 3.2 g of dimethylacetamide was cast in athickness of 300 μm on a glass plate and was dried under reducedpressure at 70° C. for three days.

Subsequently, the resulting membrane was peeled off from the glass plateand then the membrane was treated with 1 mol/L sulfuric acid at 60° C.for one hour, so that the sulfonic group was converted to the acid form.The membrane was washed further with water until no acid was detected.The washed membrane was air dried to yield the ion exchange membrane ofComparative Example 1.

Comparative Examples 2 to 12

The composite ion exchange membranes of Comparative Examples 2 to 12were prepared in the same manner as Example 1 except that the ionexchange resin served as a material of the ion exchange membrane waschanged to the ion exchange resins of Synthesis Examples given in Table2.

Comparative Example 13

A composite ion exchange membrane was prepared in the same manner asExample 1 except that the sulfonated polyphenyl sulfone prepared by apolymerization reaction in Comparative Synthesis Example 1. The ionexchange resin of the comparative synthesis example had a high viscosityand exhibited somewhat gel-like behavior.

<Synthesis of Ion Exchange Resin>

(i) Synthesis Example 13 Synthesis of Ion Exchange Resin (1) HavingCrosslinkable Group

First, 39.30 g (80.0 mmol) of sodium4,4′-dichlorodiphenylsulphone-3,3′-disulfonate, 4.28 g (20.0 mmol) of4,4′-difluorobenzophenone, 25.63 g (100.0 mmol) of2,2-bis(4-hydroxy-3-methylphenyl)propane, 15.89 g (115.0 mmol) ofpotassium carbonate, 200 ml of N-methyl-2-pyrrolidone and 30 ml oftoluene were charged into a 1,000 ml side-arm flask equipped with anitrogen introduction tube, a stirring blade, a Dean-Stark trap and athermometer and then were heated under nitrogen flow while being stirredon an oil bath.

Subsequently, after dehydration by azeotropy with toluene was conductedat 140° C., toluene was removed completely by distillation. Thereafterthe temperature was raised to 200° C. and heating was continued for 15hours. Subsequently, the solution cooled to room temperature was pouredinto 5000 ml of pure water. Thus, an ion exchange resin wasreprecipitated. Then, the ion exchange resin filtered was dried underreduced pressure at 50° C.

The inherent viscosity of the ion exchange resin measured was 0.63 dl/g.The yield of the ion exchange resin obtained was 45.3 g (yield 74%).

(ii) Synthesis Example 14 Synthesis of Ion Exchange Resin (2) HavingCrosslinkable Group

First, 29.48 g (60.0 mmol) of sodium4,4′-dichlorodiphenylsulphone-3,3′-disulfonate, 11.49 g (40.0 mmol) of4,4′-dichlorodiphenylsulfone, 18.25 g (98.0 mmol) of 4,4′-biphenol,15.89 g (115.0 mmol) of potassium carbonate, 170 ml ofN-methyl-2-pyrrolidone and 30 ml of toluene were charged into a 1,000 mlside-arm flask equipped with a nitrogen introduction tube, a stirringblade, a Dean-Stark trap and a thermometer and then were heated undernitrogen flow while being stirred on an oil bath.

Subsequently, after dehydration by azeotropy with toluene was conductedat 140° C., toluene was removed completely by distillation. Thereafterthe temperature was raised to 200° C. and heating was continued for 15hours. Subsequently, after cooling of the reaction solution to 140° C.,0.240 g (2.0 mmol) of 4-ethynylphenol and 30 ml of toluene were addedand were stirred for additional two hours. Thereafter, the solutioncooled to room temperature was poured into 5000 ml of pure water. Thus,an ion exchange resin was reprecipitated. Then, the ion exchange resinfiltered was dried under reduced pressure at 50° C.

The inherent viscosity of the ion exchange resin measured was 0.61 dl/g.The yield of the ion exchange resin obtained was 48.0 g (yield 92%).

Example 13

First, an isotropic solution with apoly(p-phenylene-cis-benzobisoxazole) concentration of 1% by mass wasprepared by diluting a dope comprising polyphosphoric acid containing14% by mass of poly(p-phenylene-cis-benzobisoxazole) polymer having anintrinsic viscosity of 24 dL/g by addition of methane sulfonic acid.

Then, this solution was formed into a film on a glass plate heated to90° C. at a film formation rate of 5 mm/sec using an applicator with aclearance of 300 μm. The dope film formed on the glass plate was placedas it was in a thermohygrostat at 25° C. and 80% RH and was solidifiedfor one hour. The resulting film was washed with water until thewashings exhibited pH 7±0.5, yielding a support membrane.

Subsequently, the surface morphology observation by an atomic forcemicroscope and the section morphology observation by a transmissionelectron microscope of the resulting support membrane confirmed that themembrane was a porous membrane with continuous pores having openings inboth surfaces of the membrane. As a result of the measurement byobservation, the support membrane had an aperture ratio of 69% and aporosity of 98%.

The support membrane was then fixed into a stainless frame in water andwas immersed in a 25% aqueous solution of dimethylacetamide (DMAc), a50% aqueous solution of DMAc and a 75% aqueous solution of DMAc in orderfor one hour each. Finally, the support membrane was immersed in DMAc,so that the solvent contained in the support membrane was changed fromwater to DMAc.

Then, a solution containing an ion exchange resin composition wasprepared by stirring 20 g of the ion exchange resin (1) produced by apolymerization reaction in Synthesis Example 13 together with 80 g DMAcfor three days.

Subsequently, the support membrane prepared as above was immersed in asolution containing this ion exchange resin composition at 25° C. for 15hours and then was removed from the solution. The solvent in thesolution which permeated into the membrane and attached to the surfaceof the membrane was volatilized to dry by hot air.

The dried membrane was further dried at 120° C. under reduced pressureovernight and then was irradiated with light for one hour using anultraviolet lamp under nitrogen atmosphere at a condition of 50° C.while being fixed in a metal frame.

Thereafter, the membrane was treated with 1 mol/L sulfuric acid at 80°C. for one hour, so that the sulfonic group was converted to the acidform. The membrane was washed further with water until no acid wasdetected. The washed membrane was air dried to yield a composite ionexchange membrane 47 μm in thickness.

The resulting composite ion exchange membrane had an ionizable groupdensity of 2.1 meq/g and an ion exchange resin content of 93%. Thethickness of the composite layer was 14 μm.

The mass reduction of the resulting composite ion exchange membrane in awater resistance test was 0%. The composite ion exchange membrane had anion conductivity of 0.30 S/cm.

The resulting composite ion exchange membrane exhibited good waterresistance and good ion conductivity. It was soft and tough andtherefore was superior in handleability.

Example 14

First, a support membrane was prepared in the same manner as Example 13.This support membrane was then fixed into a stainless frame in water andwas immersed in a 25% aqueous solution of dimethylacetamide (DMAc), a50% aqueous solution of DMAc and a 75% aqueous solution of DMAc in orderfor one hour each. Finally, the support membrane was immersed in DMAc,so that the solvent contained in the support membrane was changed fromwater to DMAc.

Then, a solution containing an ion exchange resin composition wasprepared by stirring 20 g of the ion exchange resin (2) produced by apolymerization reaction in Synthesis Example 14 together with 80 g DMAcfor three days.

Subsequently, the support membrane was immersed in a solution containingan ion exchange resin at 25° C. for 15 hours and then was removed fromthe solution. The solvent in the solution which permeated into themembrane or attached to the surface of the membrane was volatilized todry by hot air.

The dried membrane was further dried at 70° C. under reduced pressurefor three days and then was heat treated at 200° C. for one hour undernitrogen atmosphere while being fixed in a metal frame.

Thereafter, the membrane, which was released from the frame, was treatedwith 1 mol/L sulfuric acid at 80° C. for one hour, so that the sulfonicgroup was converted to the acid form. The membrane was washed furtherwith water until no free acid was detected. Then, the membrane was airdried to yield a composite ion exchange membrane 0.0048 cm in thickness.

The resulting composite ion exchange membrane had an ionizable groupdensity of 1.9 meq/g and an ion exchange resin content of 92%. Thethickness of the composite layer was 14 μm.

The mass reduction of the resulting composite ion exchange membrane in awater resistance test was 0%. The composite ion exchange membrane had anion conductivity of 0.29 S/cm.

The resulting composite ion exchange membrane exhibited good waterresistance and good ion conductivity. It was soft and tough andtherefore was superior in handleability.

Comparative Example 14

First, a solution prepared by dissolving 0.4 g of the ion exchange resin(1) having a crosslinkable group of Synthesis Example 13 in 1.6 g ofdimethylacetamide was cast in a thickness of 300 μm on a glass plate andwas dried under reduced pressure at 70° C. for three days.

Subsequently, after being peeled off from the glass plate, the resultingmembrane was fixed into a metal frame and then was irradiated with lightat 50° C. for one hour under nitrogen atmosphere using an ultravioletlamp while being fixed in a metal frame.

Thereafter, the membrane was treated with 1 mol/L sulfuric acid at 80°C. for one hour, so that the sulfonic group was converted to the acidform. The membrane was washed further with water until no acid wasdetected. The washed membrane was air dried to yield a transparent ionexchange membrane 47 μm in thickness.

The ionizable group density of the ion exchange membrane of thiscomparative example was 2.2 meq/g.

The mass reduction in a water resistance test of the ion exchangemembrane of this comparative example was 0%. The ion exchange membranehad an ion conductivity of 0.33 S/cm. Thus, the membrane exhibitedsatisfactory water resistance and ion conductivity, but it was hard,lack of softness, and a little fragile.

Comparative Example 15

First, a solution prepared by dissolving 0.4 g of the ion exchange resin(2) having a crosslinkable group of Synthesis Example 14 in 1.6 g ofdimethylacetamide was cast in a thickness of 300 μm on a glass plate andwas dried under reduced pressure at 70° C. for three days.

Subsequently, after being peeled off from the glass plate, the resultingmembrane was fixed into a metal frame and then was treated at 200° C.for one hour under nitrogen atmosphere.

Thereafter, the membrane was treated with 1 mol/L sulfuric acid at 80°C. for one hour, so that the sulfonic group was converted to the acidform. The membrane was washed further with water until no acid wasdetected. The washed membrane was air dried to yield a transparent ionexchange membrane 49 μm in thickness.

The ionizable group density of the ion exchange membrane of thiscomparative example was 2.1 meq/g.

The mass reduction in a water resistance test of the ion exchangemembrane of this comparative example was 0%. The ion exchange membranehad an ion conductivity of 0.33 S/cm. Thus, the membrane exhibitedsatisfactory water resistance and ion conductivity, but this membranewas also hard, lack of softness, and a little fragile.

As a result, the composite ion exchange membrane or ion exchangemembranes of Comparative Examples 13 to 15 were found to be defective inat least one item among ion conductivity, swelling resistance,mechanical strength and water resistance. It, therefore, is difficult touse them suitably as a solid polymer electrolyte membrane of fuel cells.

On the other hand, the composite ion exchange membranes Examples 13 and14 are good in ion conductivity and also superior in the aspect ofcombination. Moreover, they are well inhibited with respect to swellingand are also superior in water resistance. It, therefore, has been shownthat they are composite ion exchange membranes which have goodcharacteristics and can be used suitably as a solid polymer electrolytemembrane of fuel cells.

<Measurement Methods and Evaluation Methods>

In the examples and comparative examples of the present invention,measurements and evaluations were carried out according to the methodsdescribed below. The results of the measurements and evaluationsobtained by use of these methods for measurement and evaluation areshown in Table 1 and Table 2.

(i) Measurement Method of Intrinsic Viscosity

For the polymer forming the support membrane, the viscosity of a polymersolution adjusted to have a concentration of 0.5 g/L usingmethanesulfonic acid as solvent was measured with an Ubbelohde'sviscometer in a thermostat at 25° C. and then the intrinsic viscositywas calculated.

(ii) Measurement Method of Surface Open Area Ratio of Support Membrane

The surface aperture ratio of support membranes was measured by thefollowing method.

First, water in a support membrane sample washed with water wasdisplaced by ethanol, which was then further displaced fully by isoamylacetate. The resultant was subjected to CO₂ supercritical point dryingusing a supercritical point drying apparatus (HCP-1) manufactured byHitachi, Ltd.

Subsequently, the support membrane thus supercritical point dried wasapplied with a platinum coating with a thickness of 150 angstroms andthen was subjected to scanning electron microscopic (SEM) observation atan acceleration voltage of 10 kV at a sample inclining angle of 30degrees using an SEM (S-800) manufactured by Hitachi, Ltd.

Next, as shown in FIG. 2, in a scanning electron microphotograph with amultiplication of 10,000 of the surface of the support membrane, avisual field corresponding to a square with sides having a length of 5μm was chosen and was colored into white for portions corresponding tothe outermost surface of the membrane and to black for the otherportions. Thereafter, the image was captured into a computer through animage scanner. Using image analysis software Scion Image available fromScion Corp., U.S.A., the proportion accounted for by the black portionsin the image was measured.

In FIG. 2, symbol 4 represents fibrils of a support membrane and symbol5 represents voids.

This operation was repeated three times for one sample and the averagewas used. This average was used as the surface aperture ratio of thesupport membrane.

(iii) Measurement Method of Porosity of Support Membrane

The porosity of a support membrane was determined by the followingmethod.

First, the volume Vw [mL] of the water filling the voids in the membranewas obtained by dividing the weight of water calculated from thedifference between the weight of a support membrane in awater-containing condition and an absolutely dried support membrane bythe density of water.

Subsequently, the porosity of the support membrane was determined fromVw and the volume of the membrane in a water-containing condition Vm[mL] by a calculation shown below.

Porosity of support membrane [%]=Vw/Vm×100

(iv) Measurement Method of Thickness of Each Layer ConstitutingComposite Ion Exchange Membrane

The thickness of a composite layer constituting a composite ion exchangemembrane and the thicknesses of surface layers formed on both surfacesof the composite layer, the surface layers being composed of an ionexchange resin composition containing no support membrane with thecomposite layer sandwiched therebetween, were measured in the mannermentioned below.

First, a sample block was prepared by embedding a composite ion exchangemembrane sample cut into 300 μm in width and 5 mm in length with a resinhaving a composition of Luveak-812 (available from Nacalai Tesque,Inc.)/Luveak-NMA (available from Nacalai Tesque, Inc.)/DMP30 (availablefrom TAAB)=100/89/4 and then curing it at 60° C. for 12 hours.

A tip of the block was then cut with a diamond knife (SK2045manufactured by Sumitomo Electric Industries, Ltd.) using anultramicrotome (2088ULTROTOME V manufactured by LKB) so that a smoothsection was exposed.

Subsequently, the thickness of each layer was determined byphotographing the section of the composite membrane thus exposed by anoptical microscope and then comparing it with a scale with a knownlength photographed at the same multiplication.

For example, in the case where the support has a large porosity, thereare some cases where no clear interface is formed between at least onesurface layer and a composite layer arranged inside the surface layerand the structure near the interface changes continuously. In suchcases, a portion closest to the outer surface of the composite ionexchange membrane among the portions where a continuous structuralchange can be confirmed by an optical microscope was defined as theoutermost surface of the composite layer and the distance from it to theouter surface of the composite ion exchange membrane was defined as thethickness of the surface layer.

(v) Measurement Method of Ion Conductivity

First, platinum wires (diameter: 0.2 mm) were pressed against thesurface of a strip-shaped composite ion exchange membrane sample on anown-made measuring probe (made of Teflon) and the sample was held in athermo-hygrostat oven (Nagano Science Co., Ltd., LH-20-01) underconditions of 80° C. and 95% RH for measuring complex impedance betweenthe platinum wires at 10 KHz with 1250 FREQUENCY RESPONSE ANALYSER bySOLARTRON.

In the above operations, measurement was performed while varying thedistance between wires for calculating ion conductivity by cancelingcontact resistance between a membrane and the platinum wires from aslope plotting the measured value of resistance against the wiredistance through the following equation.Ion conductivity [S/cm]=1/membrane width [cm]×membrane thickness[cm]×resistance slope [Ω/cm](vi) Measurement Method of Inherent Viscosity of Ion Exchange Resin

An ion exchange resin was dissolved in a N-methyl-2-pyrrolidone solutionso that the polymer concentration became 0.25 g/dl and the measurementwas conducted at 30° C. by use of an Ostwald viscosimeter.

(vii) Measurement Method of Ion Exchange Capacity of Composite IonExchange Membrane

First, 100 mg of composite ion exchange membrane was immersed in 50 mlof 0.01N aqueous NaOH solution and was stirred at 25° C. overnight.Then, neutralization titration was carried out using 0.05N aqueous HClsolution. In the neutralization titration, a potentiometric titratorCOMTITE-980 manufactured by Hiranuma Sangyo Co., Ltd. was used. The ionexchange capacity was calculated according to the following equation.Ion exchange capacity [meq/g]=(10−titer [ml])/2(viii) Measurement Method of Ion Exchange Resin (ICP) Content ofComposite Ion Exchange Membrane

The ion exchange resin content of composite ion exchange membranes wasmeasured by the following method.

First, the weight of a composite ion exchange membrane after 6-hourvacuum drying at 110° C., Dc [g/m²], was measured. Subsequently, asupport membrane obtained under production conditions the same as thoseused in the production of the support membrane used in the preparationof the composite ion exchange membrane was dried without being combinedwith an ion exchange resin composition and the weight of the driedsupport membrane, Ds [g/m²], was measured. Then, based on these values,the ion exchange resin content of the composite ion exchange membranewas obtained by the following calculation.Ion exchange resin content [mass %]=(Dc−Ds)/Dc×100(ix) Evaluation Method of Swellability of Composite Ion ExchangeMembrane

The swellability of composite ion exchange membranes was measured by thefollowing method.

First, a composite ion exchange membrane was treated in hot water at 80°C. for three hours and then removed. Immediately after the removal, thethickness of the composite ion exchange membrane was measured. Thechange (%) relative to the thickness of the composite ion exchangemembrane before the hot water treatment was defined as the swellabilityof the composite ion exchange membrane.

(x) Measurement of Methanol Permeability

Two glass tanks were coupled via a diaphragm made of a sample; 5Maqueous methanol solution was introduced into one of the tanks anddistilled water was introduced into the other. The methanolconcentration in the tank containing distilled water was determined atappropriate intervals. The determination of methanol was carried out bygas chromatography. The methanol concentration was calculated on thebasis of a calibration curve produced by using peak areas detected whenpredetermined concentration of methanol solutions were injected. Themethanol permeation rate was calculated from the following equation onthe basis of the slope of the resulting methanol concentrations plottedagainst elapsed time.Methanol permeation rate (mmol·m⁻²·sec⁻¹)=Slop of plots(mmol/sec)÷sample area (m²)

As can be understood from these results of measurement and evaluation,the ion exchange membranes including the ion exchange resins ofComparative Examples 1 to 12 as their only material are good withrespect to ion conductivity, but they swell heavily. It, therefore, isdifficult to use them suitably as a solid polymer electrolyte membraneof fuel cells.

Regarding the composite ion exchange membrane of Comparative Example 13,the swelling thereof is inhibited, but the combination isunsatisfactorily established and the ion conductivity is low. It istherefore difficult to use it suitably as solid polymer electrolytemembranes of fuel cells.

On the other hand, the composite ion exchange membranes of Examples 1 to12 are good in ion conductivity and also superior in the aspect ofcombination. Moreover, they are well inhibited with respect to swelling.It, therefore, has been shown that they are composite ion exchangemembranes which have good characteristics and can be used suitably assolid polymer electrolyte membranes of fuel cells. In addition, thecomposite ion exchange membranes of Examples 1 to 12 caused almost nodecrease in ion conductivity and exhibited smaller methanolpermeabilities in comparison to Comparative Example 13 which wasdirected to an ion exchange membrane composed only of the correspondingion exchange resin. In particular, the composite ion exchange membranesof Examples 4 and 10 to 12, which possess small ion exchange capacities,can be used suitably as solid polymer electrolyte membranes of directmethanol-type fuel cells because of their particularly small methanolpermeabilities.

For the composite ion exchange membranes of Example 1 and ComparativeExample 13, the distribution of ion exchange resin was evaluated.

(xi) Evaluation of Distribution of Ion Exchange Resin in Composite IonExchange Membrane (1)

By use of an electron probe microanalyzer (JXA-8900RL manufactured byJEOL), linear analysis measurement of elements which are in a compositemembrane and are contained only in the ion exchange resin was conducted.A block was prepared by embedding a composite membrane sample cut into300 μm in width and 5 mm in length with resin having a composition ofLuveak-812 (available from Nacalai Tesque, Inc.)/Luveak-NMA (availablefrom Nacalai Tesque, Inc.)/DMP30 (available from TAAB)=100/89/3 and thencuring it at 60° C. for 12 hours. A tip of the resulting block was cutwith a diamond knife (SK2045 manufactured by Sumitomo ElectricIndustries, Ltd.) using an ultramicrotome (2088ULTROTOME 5 manufacturedby LKB) so that a smooth section with a size of width 300 μm×thethickness of the composite membrane was exposed. A piece having ameasuring plane provided with an evaporated carbon film was used as asample for measurement. It was made sure that it was possible to ensurea measuring site where neither scars nor spoils are found in a measuringplane through a 500× optical microscope. Then, the number of the countedX-rays of a target element was read while the high angle back and thelow angle back were set to 5 μm and 5 μm, respectively, and the beamdiameter was set to the minimum at a spectroscope position which wasfixed so that Kα-rays among the X-rays radiated from the target elemententered an analyzing crystal at an angle satisfying the Bragg'sdiffraction condition. The measuring area was decided to be a straightline running through the composite membrane along its thicknessdirection. Regarding an accelerating voltage, an irradiation current anda measuring time, the adopted conditions were conditions such that whenfive points are chosen randomly which are on the center of the compositemembrane and are each equidistant from a membrane surface and pointanalysis is conducted in advance by using the above-mentionedspectroscopic conditions and beam diameter, measurements with avariation within 20%-CV are obtained. Among the linear analysis data,ones that take a minimum value at points which are outside the compositemembrane and which are closest to both surfaces of the compositemembrane, respectively, were connected to produce a base line, and acounted value at each point was calculated by subtracting the baselinefrom each linear analysis data. Among these, CV values were calculatedfor the values within the composite membrane. The measurement wererepeated ten times for different analysis points and the average wasused as the objective value.

Noted that when n data are collected in the region inside the compositemembrane and when a counted value after the baseline subtraction is letbe x_(i) (i=1, 2, . . . , n), the formula for calculation of CV value(%) is as follows:

CV(%) = s/ < x > ×100$s = {\sqrt{\;}\left\{ {\sum\limits_{1 = l}^{n}{\left( {{x_{i} -} < x >} \right)^{2}/\left( {n - 1} \right)}} \right\}}$<x>: Arithmetic Mean Value of all Data

The composite ion exchange membranes of Example 1 and ComparativeExample 13 were analyzed for their distribution conditions of an ionexchange resin using the number of X-rays counted with respect tosulfur, which is an element contained only in the ion exchange resin. Asa result, the variations of the number of the counted X-rays of sulfurin a composite ion exchange membrane, expressed in CV value, were 21%and 58%, respectively. The composite ion exchange membranes of thepresent invention are better membranes in comparison to composite ionexchange membranes out of the scope of the present invention because inthe composite ion exchange membranes of the present invention, ionexchange resin distributes in their composite membrane with a higheruniformity in comparison to composite ion exchange membranes out of thescope of the present invention.

(xii) Evaluation of Distribution of Ion Exchange Resin in Composite IonExchange Membrane (2)

By use of a wavelength-dispersive electron probe microanalyzer(JXA-8900RL manufactured by JEOL), linear analysis measurement ofelements which are in a composite membrane and are contained only in theion exchange resin was conducted. A sample block was prepared byembedding a composite membrane sample cut into 300 μm in width and 5 mmin length with a resin having a mixing volume ratio of Luveak-812(available from Nacalai Tesque, Inc.)/Luveak-NMA (available from NacalaiTesque, Inc.)/DMP30 (available from TAAB)=100/89/3 and then curing it at60° C. for 12 hours. A tip of the block was cut with a diamond knife(SK2045 manufactured by Sumitomo Electric Industries, Ltd.) using anultramicrotome (2088ULTROTOME V manufactured by LKB) so that a smoothsection with a size of width 300 μm×the thickness of the compositemembrane was exposed. On a measuring plane, an evaporated carbon layerwas formed in a thickness of about 200 to 300 angstroms to yield asample for measurement. It was made sure that it was possible to ensurea measuring site where neither scars nor spoils are found in a measuringplane through a 500× optical microscope. Then, the number of the countedX-rays of a target element was read while the high angle back and thelow angle back were set to 5 μm and 5 μm, respectively, and the beamdiameter was set to the minimum at a spectroscope position which wasfixed so that Kα-rays among the X-rays radiated from the target elemententered an analyzing crystal at an angle satisfying the Bragg'sdiffraction condition. The measuring area was decided to be a straightline running through the composite membrane along its thicknessdirection. Regarding an accelerating voltage, an irradiation current anda measuring time, the adopted conditions were conditions such that whenfive points are chosen randomly which are on the center of the compositemembrane and are each equidistant from a membrane surface and pointanalysis is conducted in advance by using the above-mentionedspectroscopic conditions and beam diameter, measurements with avariation within 20%-CV are obtained. Among the linear analysis data,ones that take a minimum value at points which are outside the compositemembrane and which are closest to both surfaces of the compositemembrane, respectively, were connected to produce a base line, and acounted value at each point was calculated by subtracting the baselinefrom each linear analysis data. Among these data, only the data in theregion inside the composite membrane were adopted and the number ofpoints where the value is up to 5% relative to the maximum value weredetermined. The measurement were repeated ten times for differentanalysis points and the average was used as the objective value.

Noted that when n data are collected and when a counted value is let bex_(i) (i=1, 2, . . . , n), the formula for calculation of CV value (%)is as follows:

CV(%) = s/ < x > ×100$s = {\sqrt{\;}\left\{ {\sum\limits_{1 = l}^{n}{\left( {{x_{i} -} < x >} \right)^{2}/\left( {n - 1} \right)}} \right\}}$<x>: Arithmetic Mean Value of all Data

The composite ion exchange membranes of Example 1 and ComparativeExample 13 were analyzed for their distribution conditions of an ionexchange resin using the number of X-rays counted with respect tosulfur, which is an element contained only in the ion exchange resin. Inthese membranes, the number of the analysis points where the number ofthe counted X-rays of sulfur is 5% or less relative to the maximumnumber was 2% and 42%, respectively. The composite ion exchange membraneof the present invention is superior to other composite ion exchangemembranes because it is of less nonuniformity in distribution of an ionexchange resin in the composite membrane and has almost no compositeportions containing less ion exchange resin.

Embodiments and examples disclosed this time must be considered asillustrative in all points and not restrictive. The scope of the presentinvention is shown not by the above description but by the scope ofclaim for patent, and it is intended that all modifications within themeaning and range equivalent to the scope of claim for patent areincluded.

INDUSTRIAL APPLICABILITY

From the results described above, the composite ion exchange membrane ofthe present invention is a composite ion exchange membrane having a highswelling resistance and being superior in mechanical strength and ionconductivity.

Therefore, the composite ion exchange membrane of the present inventioncan be used as a solid polymer electrolyte membrane for solid polymerfuel cells.

1. A composite ion exchange membrane comprising an ion exchange resincomposition, and a support membrane having continuous pores penetratingthe support membrane, wherein said support membrane is a supportmembrane which accepts said ion exchange resin composition within saidpore, and said ion exchange resin composition is an ion exchange resincomposition which contains an ion exchange resin including linking unitsrepresented by Chemical Formula 2A and linking units represented byChemical Formula 2B at a ratio, Chemical Formula 2A: Chemical Formula 2B=n:m,

wherein in Chemical Formulas 2A and 2B, Z represents H, Li, Na, K or acation derived from an aliphatic or aromatic amine; n represents aninteger within a range of 1 to 1000; and m represents an integer withina range of 1 to 1000, wherein the composite ion exchange membrane has asurface layer comprising said ion exchange resin composition on eachside of said support membrane, wherein the thickness of each of sidesurface layers is within a range of 1 to 50 μm and also is within arange which does not exceed half the total thickness of said compositeion exchange membrane, wherein at least one surface of said supportmembrane has an aperture ratio within a range of 40 to 95%, wherein theinherent viscosity of the ion exchange resin is not lower than 0.4 dl/gand nothigher than 1.5 dl/g, wherein the porosity of the supportmembrane is not lower than 95%, and wherein said Ar₁ in Chemical Formula2A and said Ar₃ in Chemical Formula 2B each is a linking unitrepresented by Chemical Formula 6, said Ar₂ in Chemical Formula 2B is alinking unit represented by Chemical Formula 4, and said n and said msatisfy Mathematical Expression 2:0.2 ≦n/(n+m)≦0.8 (Mathematical Expression 2)

wherein in Chemical Formula 4 and Chemical Formula 6, A represents ineach occurrence a linking site with another linking unit.
 2. A compositeion exchange membrane comprising an ion exchange resin composition, anda support membrane having continuous pores penetrating the supportmembrane, wherein said support membrane is a support membrane whichaccepts said ion exchange resin composition within said pore, and saidion exchange resin composition is an ion exchange resin compositionwhich contains an ion exchange resin including linking units representsby Chemical Formula 2A and linking units represented by Chemical Formula2B at a ratio, Chemical Formula 2A:Chemical Formula 2B =n:m,

wherein in Chemical Formulas 2A and 2B, Z represents H, Li, Na, K or acation derived from an aliphatic or aromatic amine; and n represents aninteger within a range of 1 to 1000 and m represents an integer within arange of 1 to 1000, wherein the composite ion exchange membrane has asurface layer comprising said ion exchange resin composition on eachside of said support membrane, wherein the thickness of each of sidesurface layers is a within a range of 1 to 50 μm and also is within arange which does not exceed half the total thickness of said compositeion exchange membrane, wherein at least one surface of said supportmembrane has a aperture ratio within a range of 40 to 95%, wherein theinherent viscosity of the ion exchange resin is not lower than 0.4 dl/gand not higher than 1.5 dl/g, wherein the porosity of the supportmembrane is not lower than 95%, and wherein said Ar₁ in Chemical Formula2A and said Ar₃ in Chemical Formula 2B each is a linking unitrepresented by Chemical Formula 7, said Ar₂ in Chemical Formula 2B is alinking unit represented by Chemical Formula 3, and said n and said msatisfy Mathematical Expression 3:0.3 ≦n/(n+m)≦0.7 (Mathematical Expression 3)


3. The composite ion exchange membrane according to claim 1, whereinsaid support membrane contains a polybenzazole-type polymer as amaterial.
 4. The composite ion exchange membrane according to claim 2,wherein said support membrane contains a polybenzazole-type polymer as amaterial.
 5. The composite ion exchange membrane according to claim 3,wherein said support membrane is obtained by shaping an isotropicsolution containing said polybenzazole-type polymer in a content withina range of 0.5 to 2% by mass into film and then solidifying thesolution.
 6. The composite ion exchange membrane according to claim 1,wherein when a straight line running through the composite ion exchangemembrane along its thickness direction is set in an analysis area in across section of said composite ion exchange membrane and a linearanalysis for elements contained only in the ion exchange resin isconducted using an electron probe microanalyzer, the variation in thenumber of X-ray counted, as indicated in CV value, is within 50%.
 7. Thecomposite ion exchange membrane according to claim 1, wherein when astraight line running through the composite ion exchange membrane alongits thickness direction is set in an analysis area in a cross section ofsaid composite ion exchange membrane and a linear analysis for elementscontained only in the ion exchange resin is conducted using an electronprobe microanalyzer, the number of the analysis points where the numberof the counted X-rays of the analyzed elements is 5% or less relative tothe maximum number is within a range of 0 to 30% of the number of allthe analysis points.